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python: can't open file 'test.py': [Errno 2] No such file or directory

yanghartai 2019-04-24 10:58:16

在当前目录下，运行位于另外一个目录的py文件。

C:\>python Test001.py
python: can't open file 'Test001.py': [Errno 2] No such file or directory

如果指定了文件的全路径，运行正常
C:\>python c:\testdir\Test001.py
this is a test

我试图将c:\testdir加入到系统环境变量PATH里，但是仍然报错，can't open file 'Test001.py': [Errno 2] No such file or directory

是不是如果运行的py脚本不在当前目录下，就必须要指定全路径？

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Steven·简谈 2019-04-25

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为什么有这个需求，如果是运行的话还是全路径，如果是想添加库的话就放在Python目录中的 \Lib\site-packages 文件夹下

Table of Contents Header Files The #define Guard Header File Dependencies Inline Functions The -inl.h Files Function Parameter Ordering Names and Order of Includes Scoping Namespaces Nested Classes NonmemberStatic Memberand Global Functions Local Variables Static and Global Variables Classes Doing Work in Constructors Default Constructors Explicit Constructors Copy Constructors Structs vs. Classes Inheritance Multiple Inheritance Interfaces Operator Overloading Access Control Declaration Order Write Short Functions Google-Specific Magic Smart Pointers cpplint Other C++ Features Reference Arguments Function Overloading Default Arguments Variable-Length Arrays and alloca() Friends Exceptions Run-Time Type Information (RTTI) Casting Streams Preincrement and Predecrement Use of const Integer Types 64-bit Portability Preprocessor Macros 0 and NULL sizeof Boost C++0x Naming General Naming Rules File Names Type Names Variable Names Constant Names Function Names Namespace Names Enumerator Names Macro Names Exceptions to Naming Rules Comments Comment Style File Comments Class Comments Function Comments Variable Comments Implementation Comments PunctuationSpelling and Grammar TODO Comments Deprecation Comments Formatting Line Length Non-ASCII Characters Spaces vs. Tabs Function Declarations and Definitions Function Calls Conditionals Loops and Switch Statements Pointer and Reference Expressions Boolean Expressions Return Values Variable and Array Initialization Preprocessor Directives Class Format Constructor Initializer Lists Namespace Formatting Horizontal Whitespace Vertical Whitespace Exceptions to the Rules Existing Non-conformant Code Windows Code Important Note Displaying Hidden Details in this Guide link ▶This guide contains many details that are initially hidden from view. They are marked by the triangle iconwhich you see here on your left. Click it now. You should see "Hooray" appear below. Hooray! Now you know you can expand points to get more details. Alternativelythere's an "expand all" at the top of this document. Background C++ is the main development language used by many of Google's open-source projects. As every C++ programmer knowsthe language has many powerful featuresbut this power brings with it complexitywhich in turn can make code more bug-prone and harder to read and maintain. The goal of this guide is to manage this complexity by describing in detail the dos and don'ts of writing C++ code. These rules exist to keep the code base manageable while still allowing coders to use C++ language features productively. Stylealso known as readabilityis what we call the conventions that govern our C++ code. The term Style is a bit of a misnomersince these conventions cover far more than just source file formatting. One way in which we keep the code base manageable is by enforcing consistency. It is very important that any programmer be able to look at another's code and quickly understand it. Maintaining a uniform and following conventions means that we can more easily use "pattern-matching" to infer what various symbols are and what invariants are true about them. Creating commonrequired idioms and patterns makes code much easier to understand. In some cases there might be good arguments for changing certain rulesbut we nonetheless keep things as they are in order to preserve consistency. Another issue this guide addresses is that of C++ feature bloat. C++ is a huge language with many advanced features. In some cases we constrainor even banuse of certain features. We do this to keep code simple and to avoid the various common errors and problems that these features can cause. This guide lists these features and explains why their use is restricted. Open-source projects developed by Google conform to the requirements in this guide. Note that this guide is not a C++ tutorial: we assume that the reader is familiar with the language. Header Files In generalevery .cc file should have an associated .h file. There are some common exceptionssuch as unittests and small .cc files containing just a main() function. Correct use of header files can make a huge difference to the readabilitysize and performance of your code. The following rules will guide you through the various pitfalls of using header files. The #define Guard link ▶All header files should have #define guards to prevent multiple inclusion. The format of the symbol name should be ___H_. To guarantee uniquenessthey should be based on the full path in a project's source tree. For examplethe file foo/src/bar/baz.h in project foo should have the following guard: #ifndef FOO_BAR_BAZ_H_ #define FOO_BAR_BAZ_H_ ... #endif // FOO_BAR_BAZ_H_ Header File Dependencies link ▶Don't use an #include when a forward declaration would suffice. When you include a header file you introduce a dependency that will cause your code to be recompiled whenever the header file changes. If your header file includes other header filesany change to those files will cause any code that includes your header to be recompiled. Thereforewe prefer to minimize includesparticularly includes of header files in other header files. You can significantly minimize the number of header files you need to include in your own header files by using forward declarations. For exampleif your header file uses the File class in ways that do not require access to the declaration of the File classyour header file can just forward declare class File; instead of having to #include "file/base/file.h". How can we use a class Foo in a header file without access to its definition? We can declare data members of type Foo* or Foo&. We can declare (but not define) functions with argumentsand/or return valuesof type Foo. (One exception is if an argument Foo or const Foo& has a non-explicitone-argument constructorin which case we need the full definition to support automatic type conversion.) We can declare static data members of type Foo. This is because static data members are defined outside the class definition. On the other handyou must include the header file for Foo if your class subclasses Foo or has a data member of type Foo. Sometimes it makes sense to have pointer (or betterscoped_ptr) members instead of object members. Howeverthis complicates code readability and imposes a performance penaltyso avoid doing this transformation if the only purpose is to minimize includes in header files. Of course.cc files typically do require the definitions of the classes they useand usually have to include several header files. Note: If you use a symbol Foo in your source fileyou should bring in a definition for Foo yourselfeither via an #include or via a forward declaration. Do not depend on the symbol being brought in transitively via headers not directly included. One exception is if Foo is used in myfile.ccit's ok to #include (or forward-declare) Foo in myfile.hinstead of myfile.cc. Inline Functions link ▶Define functions inline only when they are smallsay10 lines or less. Definition: You can declare functions in a way that allows the compiler to expand them inline rather than calling them through the usual function call mechanism. Pros: Inlining a function can generate more efficient object codeas long as the inlined function is small. Feel free to inline accessors and mutatorsand other shortperformance-critical functions. Cons: Overuse of inlining can actually make programs slower. Depending on a function's sizeinlining it can cause the code size to increase or decrease. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size. On modern processors smaller code usually runs faster due to better use of the instruction cache. Decision: A decent rule of thumb is to not inline a function if it is more than 10 lines long. Beware of destructorswhich are often longer than they appear because of implicit member- and base-destructor calls! Another useful rule of thumb: it's typically not cost effective to inline functions with loops or switch statements (unlessin the common casethe loop or switch statement is never executed). It is important to know that functions are not always inlined even if they are declared as such; for examplevirtual and recursive functions are not normally inlined. Usually recursive functions should not be inline. The main reason for making a virtual function inline is to place its definition in the classeither for convenience or to document its behaviore.g.for accessors and mutators. The -inl.h Files link ▶You may use file names with a -inl.h suffix to define complex inline functions when needed. The definition of an inline function needs to be in a header fileso that the compiler has the definition available for inlining at the call sites. Howeverimplementation code properly belongs in .cc filesand we do not like to have much actual code in .h files unless there is a readability or performance advantage. If an inline function definition is shortwith very littleif anylogic in ityou should put the code in your .h file. For exampleaccessors and mutators should certainly be inside a class definition. More complex inline functions may also be put in a .h file for the convenience of the implementer and callersthough if this makes the .h file too unwieldy you can instead put that code in a separate -inl.h file. This separates the implementation from the class definitionwhile still allowing the implementation to be included where necessary. Another use of -inl.h files is for definitions of function templates. This can be used to keep your template definitions easy to read. Do not forget that a -inl.h file requires a #define guard just like any other header file. Function Parameter Ordering link ▶When defining a functionparameter order is: inputsthen outputs. Parameters to C/C++ functions are either input to the functionoutput from the functionor both. Input parameters are usually values or const referenceswhile output and input/output parameters will be non-const pointers. When ordering function parametersput all input-only parameters before any output parameters. In particulardo not add new parameters to the end of the function just because they are new; place new input-only parameters before the output parameters. This is not a hard-and-fast rule. Parameters that are both input and output (often classes/structs) muddy the watersandas alwaysconsistency with related functions may require you to bend the rule. Names and Order of Includes link ▶Use standard order for readability and to avoid hidden dependencies: C libraryC++ libraryother libraries' .hyour project's .h. All of a project's header files should be listed as descentants of the project's source directory without use of UNIX directory shortcuts . (the current directory) or .. (the parent directory). For examplegoogle-awesome-project/src/base/logging.h should be included as #include "base/logging.h" In dir/foo.ccwhose main purpose is to implement or test the stuff in dir2/foo2.horder your includes as follows: dir2/foo2.h (preferred location — see details below). C system files. C++ system files. Other libraries' .h files. Your project's .h files. The preferred ordering reduces hidden dependencies. We want every header file to be compilable on its own. The easiest way to achieve this is to make sure that every one of them is the first .h file #included in some .cc. dir/foo.cc and dir2/foo2.h are often in the same directory (e.g. base/basictypes_test.cc and base/basictypes.h)but can be in different directories too. Within each section it is nice to order the includes alphabetically. For examplethe includes in google-awesome-project/src/foo/internal/fooserver.cc might look like this: #include "foo/public/fooserver.h" // Preferred location. #include #include #include #include #include "base/basictypes.h" #include "base/commandlineflags.h" #include "foo/public/bar.h" Scoping Namespaces link ▶Unnamed namespaces in .cc files are encouraged. With named namespaceschoose the name based on the projectand possibly its path. Do not use a using-directive. Definition: Namespaces subdivide the global scope into distinctnamed scopesand so are useful for preventing name collisions in the global scope. Pros: Namespaces provide a (hierarchical) axis of namingin addition to the (also hierarchical) name axis provided by classes. For exampleif two different projects have a class Foo in the global scopethese symbols may collide at compile time or at runtime. If each project places their code in a namespaceproject1::Foo and project2::Foo are now distinct symbols that do not collide. Cons: Namespaces can be confusingbecause they provide an additional (hierarchical) axis of namingin addition to the (also hierarchical) name axis provided by classes. Use of unnamed spaces in header files can easily cause violations of the C++ One Definition Rule (ODR). Decision: Use namespaces according to the policy described below. Unnamed Namespaces Unnamed namespaces are allowed and even encouraged in .cc filesto avoid runtime naming conflicts: namespace { // This is in a .cc file. // The content of a namespace is not indented enum { kUnusedkEOFkError }; // Commonly used tokens. bool AtEof() { return pos_ == kEOF; } // Uses our namespace's EOF. } // namespace Howeverfile-scope declarations that are associated with a particular class may be declared in that class as typesstatic data members or static member functions rather than as members of an unnamed namespace. Terminate the unnamed namespace as shownwith a comment // namespace. Do not use unnamed namespaces in .h files. Named Namespaces Named namespaces should be used as follows: Namespaces wrap the entire source file after includesgflags definitions/declarationsand forward declarations of classes from other namespaces: // In the .h file namespace mynamespace { // All declarations are within the namespace scope. // Notice the lack of indentation. class MyClass { public: ... void Foo(); }; } // namespace mynamespace // In the .cc file namespace mynamespace { // Definition of functions is within scope of the namespace. void MyClass::Foo() { ... } } // namespace mynamespace The typical .cc file might have more complex detailincluding the need to reference classes in other namespaces. #include "a.h" DEFINE_bool(someflagfalse"dummy flag"); class C; // Forward declaration of class C in the global namespace. namespace a { class A; } // Forward declaration of a::A. namespace b { ...code for b... // Code goes against the left margin. } // namespace b Do not declare anything in namespace stdnot even forward declarations of standard library classes. Declaring entities in namespace std is undefined behaviori.e.not portable. To declare entities from the standard libraryinclude the appropriate header file. You may not use a using-directive to make all names from a namespace available. // Forbidden -- This pollutes the namespace. using namespace foo; You may use a using-declaration anywhere in a .cc fileand in functionsmethods or classes in .h files. // OK in .cc files. // Must be in a functionmethod or class in .h files. using ::foo::bar; Namespace aliases are allowed anywhere in a .cc fileanywhere inside the named namespace that wraps an entire .h fileand in functions and methods. // Shorten access to some commonly used names in .cc files. namespace fbz = ::foo::bar::baz; // Shorten access to some commonly used names (in a .h file). namespace librarian { // The following alias is available to all files including // this header (in namespace librarian): // alias names should therefore be chosen consistently // within a project. namespace pd_s = ::pipeline_diagnostics::sidetable; inline void my_inline_function() { // namespace alias local to a function (or method). namespace fbz = ::foo::bar::baz; ... } } // namespace librarian Note that an alias in a .h file is visible to everyone #including that fileso public headers (those available outside a project) and headers transitively #included by themshould avoid defining aliasesas part of the general goal of keeping public APIs as small as possible. Nested Classes link ▶Although you may use public nested classes when they are part of an interfaceconsider a namespace to keep declarations out of the global scope. Definition: A class can define another class within it; this is also called a member class. class Foo { private: // Bar is a member classnested within Foo. class Bar { ... }; }; Pros: This is useful when the nested (or member) class is only used by the enclosing class; making it a member puts it in the enclosing class scope rather than polluting the outer scope with the class name. Nested classes can be forward declared within the enclosing class and then defined in the .cc file to avoid including the nested class definition in the enclosing class declarationsince the nested class definition is usually only relevant to the implementation. Cons: Nested classes can be forward-declared only within the definition of the enclosing class. Thusany header file manipulating a Foo::Bar* pointer will have to include the full class declaration for Foo. Decision: Do not make nested classes public unless they are actually part of the interfacee.g.a class that holds a set of options for some method. NonmemberStatic Memberand Global Functions link ▶Prefer nonmember functions within a namespace or static member functions to global functions; use completely global functions rarely. Pros: Nonmember and static member functions can be useful in some situations. Putting nonmember functions in a namespace avoids polluting the global namespace. Cons: Nonmember and static member functions may make more sense as members of a new classespecially if they access external resources or have significant dependencies. Decision: Sometimes it is usefulor even necessaryto define a function not bound to a class instance. Such a function can be either a static member or a nonmember function. Nonmember functions should not depend on external variablesand should nearly always exist in a namespace. Rather than creating classes only to group static member functions which do not share static datause namespaces instead. Functions defined in the same compilation unit as production classes may introduce unnecessary coupling and link-time dependencies when directly called from other compilation units; static member functions are particularly susceptible to this. Consider extracting a new classor placing the functions in a namespace possibly in a separate library. If you must define a nonmember function and it is only needed in its .cc fileuse an unnamed namespace or static linkage (eg static int Foo() {...}) to limit its scope. Local Variables link ▶Place a function's variables in the narrowest scope possibleand initialize variables in the declaration. C++ allows you to declare variables anywhere in a function. We encourage you to declare them in as local a scope as possibleand as close to the first use as possible. This makes it easier for the reader to find the declaration and see what type the variable is and what it was initialized to. In particularinitialization should be used instead of declaration and assignmente.g. int i; i = f(); // Bad -- initialization separate from declaration. int j = g(); // Good -- declaration has initialization. Note that gcc implements for (int i = 0; i < 10; ++i) correctly (the scope of i is only the scope of the for loop)so you can then reuse i in another for loop in the same scope. It also correctly scopes declarations in if and while statementse.g. while (const char* p = strchr(str'/')) str = p + 1; There is one caveat: if the variable is an objectits constructor is invoked every time it enters scope and is createdand its destructor is invoked every time it goes out of scope. // Inefficient implementation: for (int i = 0; i < 1000000; ++i) { Foo f; // My ctor and dtor get called 1000000 times each. f.DoSomething(i); } It may be more efficient to declare such a variable used in a loop outside that loop: Foo f; // My ctor and dtor get called once each. for (int i = 0; i < 1000000; ++i) { f.DoSomething(i); } Static and Global Variables link ▶Static or global variables of class type are forbidden: they cause hard-to-find bugs due to indeterminate order of construction and destruction. Objects with static storage durationincluding global variablesstatic variablesstatic class member variablesand function static variablesmust be Plain Old Data (POD): only intscharsfloatsor pointersor arrays/structs of POD. The order in which class constructors and initializers for static variables are called is only partially specified in C++ and can even change from build to buildwhich can cause bugs that are difficult to find. Therefore in addition to banning globals of class typewe do not allow static POD variables to be initialized with the result of a functionunless that function (such as getenv()or getpid()) does not itself depend on any other globals. Likewisethe order in which destructors are called is defined to be the reverse of the order in which the constructors were called. Since constructor order is indeterminateso is destructor order. For exampleat program-end time a static variable might have been destroyedbut code still running -- perhaps in another thread -- tries to access it and fails. Or the destructor for a static 'string' variable might be run prior to the destructor for another variable that contains a reference to that string. As a result we only allow static variables to contain POD data. This rule completely disallows vector (use C arrays instead)or string (use const char []). If you need a static or global variable of a class typeconsider initializing a pointer (which will never be freed)from either your main() function or from pthread_once(). Note that this must be a raw pointernot a "smart" pointersince the smart pointer's destructor will have the order-of-destructor issue that we are trying to avoid. Classes Classes are the fundamental unit of code in C++. Naturallywe use them extensively. This section lists the main dos and don'ts you should follow when writing a class. Doing Work in Constructors link ▶In generalconstructors should merely set member variables to their initial values. Any complex initialization should go in an explicit Init() method. Definition: It is possible to perform initialization in the body of the constructor. Pros: Convenience in typing. No need to worry about whether the class has been initialized or not. Cons: The problems with doing work in constructors are: There is no easy way for constructors to signal errorsshort of using exceptions (which are forbidden). If the work failswe now have an object whose initialization code failedso it may be an indeterminate state. If the work calls virtual functionsthese calls will not get dispatched to the subclass implementations. Future modification to your class can quietly introduce this problem even if your class is not currently subclassedcausing much confusion. If someone creates a global variable of this type (which is against the rulesbut still)the constructor code will be called before main()possibly breaking some implicit assumptions in the constructor code. For instancegflags will not yet have been initialized. Decision: If your object requires non-trivial initializationconsider having an explicit Init() method. In particularconstructors should not call virtual functionsattempt to raise errorsaccess potentially uninitialized global variablesetc. Default Constructors link ▶You must define a default constructor if your class defines member variables and has no other constructors. Otherwise the compiler will do it for youbadly. Definition: The default constructor is called when we new a class object with no arguments. It is always called when calling new[] (for arrays). Pros: Initializing structures by defaultto hold "impossible" valuesmakes debugging much easier. Cons: Extra work for youthe code writer. Decision: If your class defines member variables and has no other constructors you must define a default constructor (one that takes no arguments). It should preferably initialize the object in such a way that its internal state is consistent and valid. The reason for this is that if you have no other constructors and do not define a default constructorthe compiler will generate one for you. This compiler generated constructor may not initialize your object sensibly. If your class inherits from an existing class but you add no new member variablesyou are not required to have a default constructor. Explicit Constructors link ▶Use the C++ keyword explicit for constructors with one argument. Definition: Normallyif a constructor takes one argumentit can be used as a conversion. For instanceif you define Foo::Foo(string name) and then pass a string to a function that expects a Foothe constructor will be called to convert the string into a Foo and will pass the Foo to your function for you. This can be convenient but is also a source of trouble when things get converted and new objects created without you meaning them to. Declaring a constructor explicit prevents it from being invoked implicitly as a conversion. Pros: Avoids undesirable conversions. Cons: None. Decision: We require all single argument constructors to be explicit. Always put explicit in front of one-argument constructors in the class definition: explicit Foo(string name); The exception is copy constructorswhichin the rare cases when we allow themshould probably not be explicit. Classes that are intended to be transparent wrappers around other classes are also exceptions. Such exceptions should be clearly marked with comments. Copy Constructors link ▶Provide a copy constructor and assignment operator only when necessary. Otherwisedisable them with DISALLOW_COPY_AND_ASSIGN. Definition: The copy constructor and assignment operator are used to create copies of objects. The copy constructor is implicitly invoked by the compiler in some situationse.g. passing objects by value. Pros: Copy constructors make it easy to copy objects. STL containers require that all contents be copyable and assignable. Copy constructors can be more efficient than CopyFrom()- workarounds because they combine construction with copyingthe compiler can elide them in some contextsand they make it easier to avoid heap allocation. Cons: Implicit copying of objects in C++ is a rich source of bugs and of performance problems. It also reduces readabilityas it becomes hard to track which objects are being passed around by value as opposed to by referenceand therefore where changes to an object are reflected. Decision: Few classes need to be copyable. Most should have neither a copy constructor nor an assignment operator. In many situationsa pointer or reference will work just as well as a copied valuewith better performance. For exampleyou can pass function parameters by reference or pointer instead of by valueand you can store pointers rather than objects in an STL container. If your class needs to be copyableprefer providing a copy methodsuch as CopyFrom() or Clone()rather than a copy constructorbecause such methods cannot be invoked implicitly. If a copy method is insufficient in your situation (e.g. for performance reasonsor because your class needs to be stored by value in an STL container)provide both a copy constructor and assignment operator. If your class does not need a copy constructor or assignment operatoryou must explicitly disable them. To do soadd dummy declarations for the copy constructor and assignment operator in the private: section of your classbut do not provide any corresponding definition (so that any attempt to use them results in a link error). For conveniencea DISALLOW_COPY_AND_ASSIGN macro can be used: // A macro to disallow the copy constructor and operator= functions // This should be used in the private: declarations for a class #define DISALLOW_COPY_AND_ASSIGN(TypeName) \ TypeName(const TypeName&); \ void operator=(const TypeName&) Thenin class Foo: class Foo { public: Foo(int f); ~Foo(); private: DISALLOW_COPY_AND_ASSIGN(Foo); }; Structs vs. Classes link ▶Use a struct only for passive objects that carry data; everything else is a class. The struct and class keywords behave almost identically in C++. We add our own semantic meanings to each keywordso you should use the appropriate keyword for the data-type you're defining. structs should be used for passive objects that carry dataand may have associated constantsbut lack any functionality other than access/setting the data members. The accessing/setting of fields is done by directly accessing the fields rather than through method invocations. Methods should not provide behavior but should only be used to set up the data memberse.g.constructordestructorInitialize()Reset()Validate(). If more functionality is requireda class is more appropriate. If in doubtmake it a class. For consistency with STLyou can use struct instead of class for functors and traits. Note that member variables in structs and classes have different naming rules. Inheritance link ▶Composition is often more appropriate than inheritance. When using inheritancemake it public. Definition: When a sub-class inherits from a base classit includes the definitions of all the data and operations that the parent base class defines. In practiceinheritance is used in two major ways in C++: implementation inheritancein which actual code is inherited by the childand interface inheritancein which only method names are inherited. Pros: Implementation inheritance reduces code size by re-using the base class code as it specializes an existing type. Because inheritance is a compile-time declarationyou and the compiler can understand the operation and detect errors. Interface inheritance can be used to programmatically enforce that a class expose a particular API. Againthe compiler can detect errorsin this casewhen a class does not define a necessary method of the API. Cons: For implementation inheritancebecause the code implementing a sub-class is spread between the base and the sub-classit can be more difficult to understand an implementation. The sub-class cannot override functions that are not virtualso the sub-class cannot change implementation. The base class may also define some data membersso that specifies physical layout of the base class. Decision: All inheritance should be public. If you want to do private inheritanceyou should be including an instance of the base class as a member instead. Do not overuse implementation inheritance. Composition is often more appropriate. Try to restrict use of inheritance to the "is-a" case: Bar subclasses Foo if it can reasonably be said that Bar "is a kind of" Foo. Make your destructor virtual if necessary. If your class has virtual methodsits destructor should be virtual. Limit the use of protected to those member functions that might need to be accessed from subclasses. Note that data members should be private. When redefining an inherited virtual functionexplicitly declare it virtual in the declaration of the derived class. Rationale: If virtual is omittedthe reader has to check all ancestors of the class in question to determine if the function is virtual or not. Multiple Inheritance link ▶Only very rarely is multiple implementation inheritance actually useful. We allow multiple inheritance only when at most one of the base classes has an implementation; all other base classes must be pure interface classes tagged with the Interface suffix. Definition: Multiple inheritance allows a sub-class to have more than one base class. We distinguish between base classes that are pure interfaces and those that have an implementation. Pros: Multiple implementation inheritance may let you re-use even more code than single inheritance (see Inheritance). Cons: Only very rarely is multiple implementation inheritance actually useful. When multiple implementation inheritance seems like the solutionyou can usually find a differentmore explicitand cleaner solution. Decision: Multiple inheritance is allowed only when all superclasseswith the possible exception of the first oneare pure interfaces. In order to ensure that they remain pure interfacesthey must end with the Interface suffix. Note: There is an exception to this rule on Windows. Interfaces link ▶Classes that satisfy certain conditions are allowedbut not requiredto end with an Interface suffix. Definition: A class is a pure interface if it meets the following requirements: It has only public pure virtual ("= 0") methods and static methods (but see below for destructor). It may not have non-static data members. It need not have any constructors defined. If a constructor is providedit must take no arguments and it must be protected. If it is a subclassit may only be derived from classes that satisfy these conditions and are tagged with the Interface suffix. An interface class can never be directly instantiated because of the pure virtual method(s) it declares. To make sure all implementations of the interface can be destroyed correctlythey must also declare a virtual destructor (in an exception to the first rulethis should not be pure). See StroustrupThe C++ Programming Language3rd editionsection 12.4 for details. Pros: Tagging a class with the Interface suffix lets others know that they must not add implemented methods or non static data members. This is particularly important in the case of multiple inheritance. Additionallythe interface concept is already well-understood by Java programmers. Cons: The Interface suffix lengthens the class namewhich can make it harder to read and understand. Alsothe interface property may be considered an implementation detail that shouldn't be exposed to clients. Decision: A class may end with Interface only if it meets the above requirements. We do not require the conversehowever: classes that meet the above requirements are not required to end with Interface. Operator Overloading link ▶Do not overload operators except in rarespecial circumstances. Definition: A class can define that operators such as + and / operate on the class as if it were a built-in type. Pros: Can make code appear more intuitive because a class will behave in the same way as built-in types (such as int). Overloaded operators are more playful names for functions that are less-colorfully namedsuch as Equals() or Add(). For some template functions to work correctlyyou may need to define operators. Cons: While operator overloading can make code more intuitiveit has several drawbacks: It can fool our intuition into thinking that expensive operations are cheapbuilt-in operations. It is much harder to find the call sites for overloaded operators. Searching for Equals() is much easier than searching for relevant invocations of ==. Some operators work on pointers toomaking it easy to introduce bugs. Foo + 4 may do one thingwhile &Foo + 4 does something totally different. The compiler does not complain for either of thesemaking this very hard to debug. Overloading also has surprising ramifications. For instanceif a class overloads unary operator&it cannot safely be forward-declared. Decision: In generaldo not overload operators. The assignment operator (operator=)in particularis insidious and should be avoided. You can define functions like Equals() and CopyFrom() if you need them. Likewiseavoid the dangerous unary operator& at all costsif there's any possibility the class might be forward-declared. Howeverthere may be rare cases where you need to overload an operator to interoperate with templates or "standard" C++ classes (such as operator<<(ostream&const T&) for logging). These are acceptable if fully justifiedbut you should try to avoid these whenever possible. In particulardo not overload operator== or operator< just so that your class can be used as a key in an STL container; insteadyou should create equality and comparison functor types when declaring the container. Some of the STL algorithms do require you to overload operator==and you may do so in these casesprovided you document why. See also Copy Constructors and Function Overloading. Access Control link ▶Make data members privateand provide access to them through accessor functions as needed (for technical reasonswe allow data members of a test fixture class to be protected when using Google Test). Typically a variable would be called foo_ and the accessor function foo(). You may also want a mutator function set_foo(). Exception: static const data members (typically called kFoo) need not be private. The definitions of accessors are usually inlined in the header file. See also Inheritance and Function Names. Declaration Order link ▶Use the specified order of declarations within a class: public: before private:methods before data members (variables)etc. Your class definition should start with its public: sectionfollowed by its protected: section and then its private: section. If any of these sections are emptyomit them. Within each sectionthe declarations generally should be in the following order: Typedefs and Enums Constants (static const data members) Constructors Destructor Methodsincluding static methods Data Members (except static const data members) Friend declarations should always be in the private sectionand the DISALLOW_COPY_AND_ASSIGN macro invocation should be at the end of the private: section. It should be the last thing in the class. See Copy Constructors. Method definitions in the corresponding .cc file should be the same as the declaration orderas much as possible. Do not put large method definitions inline in the class definition. Usuallyonly trivial or performance-criticaland very shortmethods may be defined inline. See Inline Functions for more details. Write Short Functions link ▶Prefer small and focused functions. We recognize that long functions are sometimes appropriateso no hard limit is placed on functions length. If a function exceeds about 40 linesthink about whether it can be broken up without harming the structure of the program. Even if your long function works perfectly nowsomeone modifying it in a few months may add new behavior. This could result in bugs that are hard to find. Keeping your functions short and simple makes it easier for other people to read and modify your code. You could find long and complicated functions when working with some code. Do not be intimidated by modifying existing code: if working with such a function proves to be difficultyou find that errors are hard to debugor you want to use a piece of it in several different contextsconsider breaking up the function into smaller and more manageable pieces. Google-Specific Magic There are various tricks and utilities that we use to make C++ code more robustand various ways we use C++ that may differ from what you see elsewhere. Smart Pointers link ▶If you actually need pointer semanticsscoped_ptr is great. You should only use std::tr1::shared_ptr under very specific conditionssuch as when objects need to be held by STL containers. You should never use auto_ptr. "Smart" pointers are objects that act like pointers but have added semantics. When a scoped_ptr is destroyedfor instanceit deletes the object it's pointing to. shared_ptr is the same waybut implements reference-counting so only the last pointer to an object deletes it. Generally speakingwe prefer that we design code with clear object ownership. The clearest object ownership is obtained by using an object directly as a field or local variablewithout using pointers at all. On the other extremeby their very definitionreference counted pointers are owned by nobody. The problem with this design is that it is easy to create circular references or other strange conditions that cause an object to never be deleted. It is also slow to perform atomic operations every time a value is copied or assigned. Although they are not recommendedreference counted pointers are sometimes the simplest and most elegant way to solve a problem. cpplint link ▶Use cpplint.py to detect errors. cpplint.py is a tool that reads a source file and identifies many errors. It is not perfectand has both false positives and false negativesbut it is still a valuable tool. False positives can be ignored by putting // NOLINT at the end of the line. Some projects have instructions on how to run cpplint.py from their project tools. If the project you are contributing to does notyou can download cpplint.py separately. Other C++ Features Reference Arguments link ▶All parameters passed by reference must be labeled const. Definition: In Cif a function needs to modify a variablethe parameter must use a pointereg int foo(int *pval). In C++the function can alternatively declare a reference parameter: int foo(int &val). Pros: Defining a parameter as reference avoids ugly code like (*pval)++. Necessary for some applications like copy constructors. Makes it clearunlike with pointersthat NULL is not a possible value. Cons: References can be confusingas they have value syntax but pointer semantics. Decision: Within function parameter lists all references must be const: void Foo(const string &instring *out); In fact it is a very strong convention in Google code that input arguments are values or const references while output arguments are pointers. Input parameters may be const pointersbut we never allow non-const reference parameters. One case when you might want an input parameter to be a const pointer is if you want to emphasize that the argument is not copiedso it must exist for the lifetime of the object; it is usually best to document this in comments as well. STL adapters such as bind2nd and mem_fun do not permit reference parametersso you must declare functions with pointer parameters in these casestoo. Function Overloading link ▶Use overloaded functions (including constructors) only if a reader looking at a call site can get a good idea of what is happening without having to first figure out exactly which overload is being called. Definition: You may write a function that takes a const string& and overload it with another that takes const char*. class MyClass { public: void Analyze(const string &text); void Analyze(const char *textsize_t textlen); }; Pros: Overloading can make code more intuitive by allowing an identically-named function to take different arguments. It may be necessary for templatized codeand it can be convenient for Visitors. Cons: If a function is overloaded by the argument types alonea reader may have to understand C++'s complex matching rules in order to tell what's going on. Also many people are confused by the semantics of inheritance if a derived class overrides only some of the variants of a function. Decision: If you want to overload a functionconsider qualifying the name with some information about the argumentse.g.AppendString()AppendInt() rather than just Append(). Default Arguments link ▶We do not allow default function parametersexcept in a few uncommon situations explained below. Pros: Often you have a function that uses lots of default valuesbut occasionally you want to override the defaults. Default parameters allow an easy way to do this without having to define many functions for the rare exceptions. Cons: People often figure out how to use an API by looking at existing code that uses it. Default parameters are more difficult to maintain because copy-and-paste from previous code may not reveal all the parameters. Copy-and-pasting of code segments can cause major problems when the default arguments are not appropriate for the new code. Decision: Except as described belowwe require all arguments to be explicitly specifiedto force programmers to consider the API and the values they are passing for each argument rather than silently accepting defaults they may not be aware of. One specific exception is when default arguments are used to simulate variable-length argument lists. // Support up to 4 params by using a default empty AlphaNum. string StrCat(const AlphaNum &a, const AlphaNum &b = gEmptyAlphaNum, const AlphaNum &c = gEmptyAlphaNum, const AlphaNum &d = gEmptyAlphaNum); Variable-Length Arrays and alloca() link ▶We do not allow variable-length arrays or alloca(). Pros: Variable-length arrays have natural-looking syntax. Both variable-length arrays and alloca() are very efficient. Cons: Variable-length arrays and alloca are not part of Standard C++. More importantlythey allocate a data-dependent amount of stack space that can trigger difficult-to-find memory overwriting bugs: "It ran fine on my machinebut dies mysteriously in production". Decision: Use a safe allocator insteadsuch as scoped_ptr/scoped_array. Friends link ▶We allow use of friend classes and functionswithin reason. Friends should usually be defined in the same file so that the reader does not have to look in another file to find uses of the private members of a class. A common use of friend is to have a FooBuilder class be a friend of Foo so that it can construct the inner state of Foo correctlywithout exposing this state to the world. In some cases it may be useful to make a unittest class a friend of the class it tests. Friends extendbut do not breakthe encapsulation boundary of a class. In some cases this is better than making a member public when you want to give only one other class access to it. Howevermost classes should interact with other classes solely through their public members. Exceptions link ▶We do not use C++ exceptions. Pros: Exceptions allow higher levels of an application to decide how to handle "can't happen" failures in deeply nested functionswithout the obscuring and error-prone bookkeeping of error codes. Exceptions are used by most other modern languages. Using them in C++ would make it more consistent with PythonJavaand the C++ that others are familiar with. Some third-party C++ libraries use exceptionsand turning them off internally makes it harder to integrate with those libraries. Exceptions are the only way for a constructor to fail. We can simulate this with a factory function or an Init() methodbut these require heap allocation or a new "invalid" staterespectively. Exceptions are really handy in testing frameworks. Cons: When you add a throw statement to an existing functionyou must examine all of its transitive callers. Either they must make at least the basic exception safety guaranteeor they must never catch the exception and be happy with the program terminating as a result. For instanceif f() calls g() calls h()and h throws an exception that f catchesg has to be careful or it may not clean up properly. More generallyexceptions make the control flow of programs difficult to evaluate by looking at code: functions may return in places you don't expect. This causes maintainability and debugging difficulties. You can minimize this cost via some rules on how and where exceptions can be usedbut at the cost of more that a developer needs to know and understand. Exception safety requires both RAII and different coding practices. Lots of supporting machinery is needed to make writing correct exception-safe code easy. Furtherto avoid requiring readers to understand the entire call graphexception-safe code must isolate logic that writes to persistent state into a "commit" phase. This will have both benefits and costs (perhaps where you're forced to obfuscate code to isolate the commit). Allowing exceptions would force us to always pay those costs even when they're not worth it. Turning on exceptions adds data to each binary producedincreasing compile time (probably slightly) and possibly increasing address space pressure. The availability of exceptions may encourage developers to throw them when they are not appropriate or recover from them when it's not safe to do so. For exampleinvalid user input should not cause exceptions to be thrown. We would need to make the guide even longer to document these restrictions! Decision: On their facethe benefits of using exceptions outweigh the costsespecially in new projects. Howeverfor existing codethe introduction of exceptions has implications on all dependent code. If exceptions can be propagated beyond a new projectit also becomes problematic to integrate the new project into existing exception-free code. Because most existing C++ code at Google is not prepared to deal with exceptionsit is comparatively difficult to adopt new code that generates exceptions. Given that Google's existing code is not exception-tolerantthe costs of using exceptions are somewhat greater than the costs in a new project. The conversion process would be slow and error-prone. We don't believe that the available alternatives to exceptionssuch as error codes and assertionsintroduce a significant burden. Our advice against using exceptions is not predicated on philosophical or moral groundsbut practical ones. Because we'd like to use our open-source projects at Google and it's difficult to do so if those projects use exceptionswe need to advise against exceptions in Google open-source projects as well. Things would probably be different if we had to do it all over again from scratch. There is an exception to this rule (no pun intended) for Windows code. Run-Time Type Information (RTTI) link ▶We do not use Run Time Type Information (RTTI). Definition: RTTI allows a programmer to query the C++ class of an object at run time. Pros: It is useful in some unittests. For exampleit is useful in tests of factory classes where the test has to verify that a newly created object has the expected dynamic type. In rare circumstancesit is useful even outside of tests. Cons: A query of type during run-time typically means a design problem. If you need to know the type of an object at runtimethat is often an indication that you should reconsider the design of your class. Decision: Do not use RTTIexcept in unittests. If you find yourself in need of writing code that behaves differently based on the class of an objectconsider one of the alternatives to querying the type. Virtual methods are the preferred way of executing different code paths depending on a specific subclass type. This puts the work within the object itself. If the work belongs outside the object and instead in some processing codeconsider a double-dispatch solutionsuch as the Visitor design pattern. This allows a facility outside the object itself to determine the type of class using the built-in type system. If you think you truly cannot use those ideasyou may use RTTI. But think twice about it. :-) Then think twice again. Do not hand-implement an RTTI-like workaround. The arguments against RTTI apply just as much to workarounds like class hierarchies with type tags. Casting link ▶Use C++ casts like static_cast(). Do not use other cast formats like int y = (int)x; or int y = int(x);. Definition: C++ introduced a different cast system from C that distinguishes the types of cast operations. Pros: The problem with C casts is the ambiguity of the operation; sometimes you are doing a conversion (e.g.(int)3.5) and sometimes you are doing a cast (e.g.(int)"hello"); C++ casts avoid this. Additionally C++ casts are more visible when searching for them. Cons: The syntax is nasty. Decision: Do not use C- casts. Insteaduse these C++- casts. Use static_cast as the equivalent of a C- cast that does value conversionor when you need to explicitly up-cast a pointer from a class to its superclass. Use const_cast to remove the const qualifier (see const). Use reinterpret_cast to do unsafe conversions of pointer types to and from integer and other pointer types. Use this only if you know what you are doing and you understand the aliasing issues. Do not use dynamic_cast except in test code. If you need to know type information at runtime in this way outside of a unittestyou probably have a design flaw. Streams link ▶Use streams only for logging. Definition: Streams are a replacement for printf() and scanf(). Pros: With streamsyou do not need to know the type of the object you are printing. You do not have problems with format strings not matching the argument list. (Though with gccyou do not have that problem with printf either.) Streams have automatic constructors and destructors that open and close the relevant files. Cons: Streams make it difficult to do functionality like pread(). Some formatting (particularly the common format string idiom %.*s) is difficult if not impossible to do efficiently using streams without using printf-like hacks. Streams do not support operator reordering (the %1s directive)which is helpful for internationalization. Decision: Do not use streamsexcept where required by a logging interface. Use printf-like routines instead. There are various pros and cons to using streamsbut in this caseas in many other casesconsistency trumps the debate. Do not use streams in your code. Extended Discussion There has been debate on this issueso this explains the reasoning in greater depth. Recall the Only One Way guiding principle: we want to make sure that whenever we do a certain type of I/Othe code looks the same in all those places. Because of thiswe do not want to allow users to decide between using streams or using printf plus Read/Write/etc. Insteadwe should settle on one or the other. We made an exception for logging because it is a pretty specialized applicationand for historical reasons. Proponents of streams have argued that streams are the obvious choice of the twobut the issue is not actually so clear. For every advantage of streams they point outthere is an equivalent disadvantage. The biggest advantage is that you do not need to know the type of the object to be printing. This is a fair point. Butthere is a downside: you can easily use the wrong typeand the compiler will not warn you. It is easy to make this kind of mistake without knowing when using streams. cout << this; // Prints the address cout << *this; // Prints the contents The compiler does not generate an error because << has been overloaded. We discourage overloading for just this reason. Some say printf formatting is ugly and hard to readbut streams are often no better. Consider the following two fragmentsboth with the same typo. Which is easier to discover? cerr << "Error connecting to '" hostname.first << ":" hostname.second << ": " hostname.firstfoo->bar()->hostname.second, strerror(errno)); And so on and so forth for any issue you might bring up. (You could argue"Things would be better with the right wrappers," but if it is true for one schemeis it not also true for the other? Alsoremember the goal is to make the language smallernot add yet more machinery that someone has to learn.) Either path would yield different advantages and disadvantagesand there is not a clearly superior solution. The simplicity doctrine mandates we settle on one of them thoughand the majority decision was on printf + read/write. Preincrement and Predecrement link ▶Use prefix form (++i) of the increment and decrement operators with iterators and other template objects. Definition: When a variable is incremented (++i or i++) or decremented (--i or i--) and the value of the expression is not usedone must decide whether to preincrement (decrement) or postincrement (decrement). Pros: When the return value is ignoredthe "pre" form (++i) is never less efficient than the "post" form (i++)and is often more efficient. This is because post-increment (or decrement) requires a copy of i to be madewhich is the value of the expression. If i is an iterator or other non-scalar typecopying i could be expensive. Since the two types of increment behave the same when the value is ignoredwhy not just always pre-increment? Cons: The tradition developedin Cof using post-increment when the expression value is not usedespecially in for loops. Some find post-increment easier to readsince the "subject" (i) precedes the "verb" (++)just like in English. Decision: For simple scalar (non-object) values there is no reason to prefer one form and we allow either. For iterators and other template typesuse pre-increment. Use of const link ▶We strongly recommend that you use const whenever it makes sense to do so. Definition: Declared variables and parameters can be preceded by the keyword const to indicate the variables are not changed (e.g.const int foo). Class functions can have the const qualifier to indicate the function does not change the state of the class member variables (e.g.class Foo { int Bar(char c) const; };). Pros: Easier for people to understand how variables are being used. Allows the compiler to do better type checkingandconceivablygenerate better code. Helps people convince themselves of program correctness because they know the functions they call are limited in how they can modify your variables. Helps people know what functions are safe to use without locks in multi-threaded programs. Cons: const is viral: if you pass a const variable to a functionthat function must have const in its prototype (or the variable will need a const_cast). This can be a particular problem when calling library functions. Decision: const variablesdata membersmethods and arguments add a level of compile-time type checking; it is better to detect errors as soon as possible. Therefore we strongly recommend that you use const whenever it makes sense to do so: If a function does not modify an argument passed by reference or by pointerthat argument should be const. Declare methods to be const whenever possible. Accessors should almost always be const. Other methods should be const if they do not modify any data membersdo not call any non-const methodsand do not return a non-const pointer or non-const reference to a data member. Consider making data members const whenever they do not need to be modified after construction. Howeverdo not go crazy with const. Something like const int * const * const x; is likely overkilleven if it accurately describes how const x is. Focus on what's really useful to know: in this caseconst int** x is probably sufficient. The mutable keyword is allowed but is unsafe when used with threadsso thread safety should be carefully considered first. Where to put the const Some people favor the form int const *foo to const int* foo. They argue that this is more readable because it's more consistent: it keeps the rule that const always follows the object it's describing. Howeverthis consistency argument doesn't apply in this casebecause the "don't go crazy" dictum eliminates most of the uses you'd have to be consistent with. Putting the const first is arguably more readablesince it follows English in putting the "adjective" (const) before the "noun" (int). That saidwhile we encourage putting const firstwe do not require it. But be consistent with the code around you! Integer Types link ▶Of the built-in C++ integer typesthe only one used is int. If a program needs a variable of a different sizeuse a precise-width integer type from such as int16_t. Definition: C++ does not specify the sizes of its integer types. Typically people assume that short is 16 bitsint is 32 bitslong is 32 bits and long long is 64 bits. Pros: Uniformity of declaration. Cons: The sizes of integral types in C++ can vary based on compiler and architecture. Decision: defines types like int16_tuint32_tint64_tetc. You should always use those in preference to shortunsigned long long and the likewhen you need a guarantee on the size of an integer. Of the C integer typesonly int should be used. When appropriateyou are welcome to use standard types like size_t and ptrdiff_t. We use int very oftenfor integers we know are not going to be too bige.g.loop counters. Use plain old int for such things. You should assume that an int is at least 32 bitsbut don't assume that it has more than 32 bits. If you need a 64-bit integer typeuse int64_t or uint64_t. For integers we know can be "big"use int64_t. You should not use the unsigned integer types such as uint32_tunless the quantity you are representing is really a bit pattern rather than a numberor unless you need defined twos-complement overflow. In particulardo not use unsigned types to say a number will never be negative. Insteaduse assertions for this. On Unsigned Integers Some peopleincluding some textbook authorsrecommend using unsigned types to represent numbers that are never negative. This is intended as a form of self-documentation. Howeverin Cthe advantages of such documentation are outweighed by the real bugs it can introduce. Consider: for (unsigned int i = foo.Length()-1; i >= 0; --i) ... This code will never terminate! Sometimes gcc will notice this bug and warn youbut often it will not. Equally bad bugs can occur when comparing signed and unsigned variables. BasicallyC's type-promotion scheme causes unsigned types to behave differently than one might expect. Sodocument that a variable is non-negative using assertions. Don't use an unsigned type. 64-bit Portability link ▶Code should be 64-bit and 32-bit friendly. Bear in mind problems of printingcomparisonsand structure alignment. printf() specifiers for some types are not cleanly portable between 32-bit and 64-bit systems. C99 defines some portable format specifiers. UnfortunatelyMSVC 7.1 does not understand some of these specifiers and the standard is missing a fewso we have to define our own ugly versions in some cases (in the of the standard include file inttypes.h): // printf macros for size_tin the of inttypes.h #ifdef _LP64 #define __PRIS_PREFIX "z" #else #define __PRIS_PREFIX #endif // Use these macros after a % in a printf format string // to get correct 32/64 bit behaviorlike this: // size_t size = records.size(); // printf("%"PRIuS"\n"size); #define PRIdS __PRIS_PREFIX "d" #define PRIxS __PRIS_PREFIX "x" #define PRIuS __PRIS_PREFIX "u" #define PRIXS __PRIS_PREFIX "X" #define PRIoS __PRIS_PREFIX "o" Type DO NOT use DO use Notes void * (or any pointer) %lx %p int64_t %qd%lld %"PRId64" uint64_t %qu%llu%llx %"PRIu64"%"PRIx64" size_t %u %"PRIuS"%"PRIxS" C99 specifies %zu ptrdiff_t %d %"PRIdS" C99 specifies %zd Note that the PRI* macros expand to independent strings which are concatenated by the compiler. Hence if you are using a non-constant format stringyou need to insert the value of the macro into the formatrather than the name. It is still possibleas usualto include length specifiersetc.after the % when using the PRI* macros. Soe.g. printf("x = %30"PRIuS"\n"x) would expand on 32-bit Linux to printf("x = %30" "u" "\n"x)which the compiler will treat as printf("x = %30u\n"x). Remember that sizeof(void *) != sizeof(int). Use intptr_t if you want a pointer-sized integer. You may need to be careful with structure alignmentsparticularly for structures being stored on disk. Any class/structure with a int64_t/uint64_t member will by default end up being 8-byte aligned on a 64-bit system. If you have such structures being shared on disk between 32-bit and 64-bit codeyou will need to ensure that they are packed the same on both architectures. Most compilers offer a way to alter structure alignment. For gccyou can use __attribute__((packed)). MSVC offers #pragma pack() and __declspec(align()). Use the LL or ULL suffixes a

最近开始学习了“笨方法学python”，在练习的第一个程序就出现了如下错误： C:\Python27\python.exe: can’t open file ‘2.py’: [Errno 2] No such file or directory。刚开始自己找了好长时间，也在网上查阅了好多资料，都没能解决，最后发觉原来是自己新建的xxx.py文件并不是像我们看到的是.py后缀的，它的后面有两层后缀，

运行Django时报错：可以尝试一下用这个命令创建app django-admin startapp app_name ‘ python manage.py startapp app_name’ 与‘ django-admin startapp app_name ’是殊途同归的。...

在终端中输入python train.py 运行训练的python文件，出现报错： python: can’t open file ‘train.py’ : [Errno 2] No such file or directory 其实是一个特别简单的错误。方法有：通过cd移动到包含该文件的上一级文件，路径中间用**/**隔开。选中包含该文件的上一级文件，右键在终端中打开，并激活进入所需的虚拟环境。再输入python train.py即可正常运行该文件。 ...

原因分析 can’t open file ‘...detect.py’