[FIXED] How to dynamically create a python function within a module?

Issue

I wrote a function def_function, that dynamically defines another function at runtime.

main.py

#!/usr/bin/python3

def def_function(name):
  lines = list()
  lines.append('global {}\n'.format(name))
  lines.append('def {}():\n'.format(name))
  lines.append('  print(\'{}() has been called!\')\n'.format(name))
  code = ''.join(lines)
  function = compile(code, '', 'exec')
  exec(function)

def_function('foo')
foo()

Running main.py gives the expected output:

foo() has been called!

Now I'd like to move the definition of def_function to module.py and import it from main.py.

module.py

def def_function(name):
  lines = list()
  lines.append('global {}\n'.format(name))
  lines.append('def {}():\n'.format(name))
  lines.append('  print(\'{}() has been called!\')\n'.format(name))
  code = ''.join(lines)
  function = compile(code, '', 'exec')
  exec(function)

main.py

#!/usr/bin/python3

from module import def_function

def_function('foo')
foo()

This results in the following error:

Traceback (most recent call last):
  File "./main.py", line 6, in <module>
    foo()
NameError: name 'foo' is not defined

I've already googled my problem and read various questions at SO, but I couldn't find a solution. Please help me.

Solution

You define foo in module.py scope. Do not forget import module.py.

Call foo(), as module.foo().

import module

module.def_function('foo')
module.foo()

May help you https://realpython.com/python-scope-legb-rule/

Additional

Add this after exec(function). Also import sys.

setattr(sys.modules['__main__'], name, globals()[name])

Setattr it's function assigns the value to the attribute of object or create new attribute. https://docs.python.org/3/library/functions.html#setattr

module.py

import sys


def def_function(name):
    lines = list()
    lines.append('global {}\n'.format(name))
    lines.append('def {}():\n'.format(name))
    lines.append('  print(\'{}() has been called!\')\n'.format(name))
    code = ''.join(lines)
    function = compile(code, '', 'exec')
    exec(function)
    setattr(sys.modules['__main__'], name, globals()[name])

main.py

from module import def_function

def_function('foo')
foo()

Answered By - fabelx

Answer Checked By - Mildred Charles (PHPFixing Admin)