Next time, please format your code examples as explained here:
About your problem: the code tries to access the function function_name in the module object, which is not what you want. function_name is a string, so you want to retrieve an attribute, the name of which you have as a string. Therefore, you need getattr(module_object, function_name)(). See the documentation for getattr:
$ python3.8
Python 3.8.2+ (heads/3.8:3e72de9e08, Apr 16 2020, 12:25:15)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> my_desired_attr = "match"
>>> re.my_desired_attr
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: module 're' has no attribute 'my_desired_attr'
>>> getattr(re, my_desired_attr)
<function match at 0x7f357ce70ee0>
>>> getattr(re, my_desired_attr)("pattern", "pattern in string")
<re.Match object; span=(0, 7), match='pattern'>