Python executable object--exec, eval, compile

Python provides a description of the built-in functions for calling executable objects, involving exec, Eval, and compile three functions. The EXEC statement is used to execute a python statement stored in a code object, a string, a file, and the eval statement is used to calculate a valid python expression stored in a code object or string, while the compile statement provides a byte-encoded precompilation.

Of course, it is important to note that the use of exec and Eval must pay attention to security issues, especially in a network environment, where others may be given the opportunity to execute illegal statements.

1.exec

Format:exec obj

The Obj object can be a string (such as a single statement, statement block), a file object, or a code object that has been precompiled by compile.

Here's an example:

examples of exec use of Python executable objectsPython

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# Single Statement string>>> exec "print ' pythoner.com '" Pythoner. COM # Multi-line statement string>>> Exec "" For i in range (5): ... print "ITER time:%d"% i... """iter time : 0 iter time : 1 iter time : 2 iter time : 3 iter time : 4

Examples of code objects are explained in part 3rd.

2.eval

Format:eval( obj[, globals=globals(), locals=locals()] )

Obj can be a string object or a code object that has been compiled by compile. Globals and locals are optional, representing objects in the global and local namespaces, where globals must be a dictionary, and locals is an arbitrary mapping object.

The following examples still illustrate:

eval of Python executable objectPython

123	>>> x = 7 >>> eval( ' 3 * x ' ) +

3.compile

Format:compile( str, file, type )

The compile statement is from type types (including ' eval ': Use with eval, ' single ': With the use of exec for a singleton statement, ' EXEC ': With the use of EXEC for multiple statements) to create the statements inside STR into code objects. File is where the code is stored, usually ".

The purpose of the compile statement is to provide a one-time bytecode compilation without having to recompile it in subsequent calls.

It is also important to note that the compile used in compile and regular expressions here are not the same, albeit for the same purpose.

Here are the corresponding examples:

compile of Python executable objectsPython

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>>> eval_code = compile( ' 1+2 ', ' ', ' Eval ') >>> eval_code <code  Object <module > at  0142abf0,  File  ",  line 1 >>> eval(eval_code) 3>>> single_code = compile( ' print ' pythoner.com "', ' , ' single ' ) >>> single_code <code Object <module> at 01c68848 , File "", line 1> >>> exec(single_code) Pythoner. COM >>> exec_code = compile("" "For I in range (5): /c16> ... print "ITER time:%d"% i "" ","' , ' exec ' ) >>> exec_code <code  Object <module > at  01c68968,  File  ",  line 1 >>> exec(exec_code) iter time : 0 iter time : 1 iter time : 2 iter time : 3 iter time : 4

Python executable object--exec, eval, compile