内部使用exec（astring）和astring中的变量定义的函数不能返回python 3中的变量

Question

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

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.

Answer 1

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

Try it using eval :

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

function('42')

returns as expected 42 .

Or simply strip that assignment:

def function(astring):
  return eval(astring)