call a function by knowing its name as a string

Problem
I want to call a function but its name is stored in a string. How to do that?

Solution
I wanted to create a menu where the user can select which entry to call. It looks like this:

(1)[r] radio
(2)[ctd] create temp. directory
--------
[m] menu
[q] <

In Python I stored it like this:

menu = OrderedDict()
menu[(1, 'r')] = ('radio', 'apps.radio.radio_player')
menu[(2, 'ctd')] = ('create temp. directory', 'apps.temp_folder.create_temp_folder')

That is, if the user selects “1“, then apps.radio.radio_player() must be called.

Here is the method that can call the appropriate function:

import importlib

def start_app(val):
    """
    Call a function by name (string).
    
    Tip from here: http://stackoverflow.com/questions/3061 .
    """ 
    _, to_call = val
    function_string = to_call # ex.: 'apps.radio.radio_player'
    mod_name, func_name = function_string.rsplit('.', 1)
    mod = importlib.import_module(mod_name)
    func = getattr(mod, func_name)
    func()

The tip is from here.

Useful Python modules

http://wiki.python.org/moin/UsefulModules

Python: 50 modules for all needs

Creating and importing a module

If you have some functions that you use often, you can collect them in a module.

mymodule.py:

def f1(n):
    return n + 1

---

How to use it (use-mymodule.py):

#!/usr/bin/env python

import mymodule

print mymodule.f1(5)      # => 6
print mymodule.__name__   # => mymodule (note that .py is missing)

---

It is also possible to add some testing code to a module:

mymodule.py:

#!/usr/bin/env python

def f1(n):
    return n + 1

if __name__ == "__main__":
    number = 1977
    print f1(number)   # => 1978

Now, you can still import it like in use-mymodule.py, or you can launch it as if it were a standalone script. In the latter case the test suite will be executed. If you import it, the test suite is not executed. A test suite is a good practice to be sure that the module is working as expected.