python函数 - exec执行函数

python函数每日一讲 - exec执行函数[Python函数]

exec 函数功能:执行储存在字符串或文件中的 Python 语句,相比于 eval,exec可以执行更复杂的 Python 代码。


This function supports dynamic execution of Python code. object must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed (unless a syntax error occurs). If it is a code object, it is simply executed. In all cases, the code that’s executed is expected to be valid as file input (see the section “File input” in the Reference Manual). Be aware that the return and yield statements may not be used outside of function definitions even within the context of code passed to the exec() function. The return value is None.

In all cases, if the optional parts are omitted, the code is executed in the current scope. If only globals is provided, it must be a dictionary, which will be used for both the global and the local variables. If globals and locals are given, they are used for the global and local variables, respectively. If provided, locals can be any mapping object. Remember that at module level, globals and locals are the same dictionary. If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition.

If the globals dictionary does not contain a value for the key __builtins__, a reference to the dictionary of the built-in module builtins is inserted under that key. That way you can control what builtins are available to the executed code by inserting your own __builtins__ dictionary into globals before passing it to exec().

注意: 在 Python2 中exec不是函数,而是一个内置语句(statement),但是Python 2中有一个 execfile() 函数。可以理解为 Python 3 把 exec 这个 statement 和 execfile() 函数的功能够整合到一个新的 exec() 函数中去了。





以下是 exec 的语法:

exec(object[, globals[, locals]])






exec 返回值永远为 None。


>>>exec 'print "Hello Python"'
Hello Python
# 单行语句字符串
>>> exec "print ''"
#  多行语句字符串
>>> 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