Python built-in function——compile

Python built-in function——compile

compilecompile(source, filename, mode[, flags[, dont_inherit,[optimize]]])
1. This function is used Compile the source code of a string, and the result can generate bytecode or AST (Abstract Syntax Tree).
Bytecode can be executed using the function exec(), and AST can be compiled using eval().
2. The parameter source is the source code of a string, or an array of AST objects.
3. The parameter filename is the file object for reading strings.
If the source code is not read from the file for compilation, then some strings used to identify these codes can be placed here.
4. The parameter mode is used to indicate the type of source code represented;
If it is an exec type, it means that this is a sequence statement that can be run;
If it is an eval type, it means that this is a single The expression statement can be used to calculate the corresponding value;
If it is a single type, it means that this is a single statement, which is executed in interactive mode.
In this case, if it is an expression, generally will output the result instead of printing it as None.
5. The optional parameters flags and dont_inherit are used to control the flags when compiling source code.
You can check the PEP236 document to learn about these parameters and related compilation instructions.
If both use default parameters (that is, both are zero values),
When calling this function for compilation, the compilation features specified in the code will be used to treat it;
If the flags parameter is set to value, and dont_inherit is not set (that is, it is zero value),
Then when compiling the code, not only the compilation features of the source code will work, but also the features specified by flags will work, which is equivalent to the union of the two;
If the parameter dont_inherit is set to have a value (that is, a non-zero value).
When compiling the statement, only the compilation feature values ​​specified by the parameter flags take effect, that is, the features specified in the source code are not used.
Compilation features are set to parameters in bitmap format, which can be viewed in __future__.
6. The optional parameter optimize is used to indicate the level of optimization used by the compiler;
The default value is -1, which means that the optimization level obtained in the command line parameter -O shall prevail;
If set The value is 0 (that is, no optimization is required, __debug__ is set to true), which means there is no optimization;
If the value is set to 1, the assert statement is deleted, and __debug__ is set to false;
If the value is set to 2, except In addition to the functions set to 1, the documentation in the code will also be deleted to achieve the best optimization results.
7. When this function compiles the code, it will return SyntaxError if there is a syntax error;
If the code contains some null bytes, it will return TypeError.
Notes:
1. When using single or eval type compilation,
If there are multiple lines of code, there must be at least one newline character \ after each line of code, otherwise a compilation prompt will be prompted when the code module is compiled. The source code is incomplete error.
After Python 3.2 version, it is allowed to enter the newline character of Windows or Mac;
2. When using exec mode, there is no need to enter the newline character after each line; after this version, optimization parameters are added.

In [16]: str = "for i in range(10): print(i)"
In [17]: c = compile(str,'','exec') #编译为字节代码对象
In [18]: exec(c)
0
1
2
3
4
5
6
7
8
9
In [19]: str = "3*x + 4*y"
In [20]: c = compile(str,'','eval') #编译为表达式
In [23]: x,y = 3,4
In [24]: eval(c)
Out[24]: 25

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