函数内部使用exec（astring）和astring中的变量定义无法在python 3中返回变量 [英] Function internally using exec(astring) with a variable definition inside astring can not return the variable in python 3

问题描述

我有一个python 3函数，它接收一串命令，说'np.pi'，然后尝试用该字符串定义一个变量。然后我尝试返回变量，但这是行不通的。

I have a python 3 function that takes a string of commands, say 'np.pi' and then tries to define a variable with that string. Then I try to return the variable, this however does not work.

input = np.pi
astring = 'funcD(funcC(funcB(funcA(input))))'

def function(astring):
  astring= 'variable = ' + astring
  exec(astring)
  return variable

In:  a = function(astring)
Out: NameError: global name 'variable' is not defined

似乎没有任何事情发生。我想要的是让该函数返回字符串中命令的输出。该字符串包含几个功能，他们之间的输入如下所示。我试着在返回后放入exec而不添加变量=，然后用函数（astring）调用函数，但那也不起作用。我相信我不能使用eval，因为我的字符串中有函数。

Nothing seems to have happened. What I would like is to have the function return the output of the command in the string. The string contains several functions who have each other as input like below. I tried putting the exec after return without adding the variable = and then call the function with a = function(astring) but that did not work either. I believe I cant use eval because my string has functions in it.

推荐答案

您没有说出您对答案的期望，所以我猜测：你想做这件事。

You didn't state what you expected from the answer, so I take a guess: You want to make this work.

使用 eval ：

def function(astring):
  astring= 'variable = ' + astring
  exec(astring)
  return eval('variable')

function('42')

按预期返回 42 。

或简单地剥离该分配：

Or simply strip that assignment:

def function(astring):
  return eval(astring)

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