Return Function description as string?

The inspect module works just fine for retrieving source code, this is not limited to older Python versions.

Provided the source is available (e.g. the function is not defined in C code or the interactive interpreter, or was imported from a module for which only the .pyc bytecode cache is available), then you can use:

import inspect
import re
import textwrap

def function_description(f):
    # remove the `def` statement.
    source = inspect.getsource(f).partition(':')[-1]
    first, _, rest = source.partition('\n')
    if not first.strip():  # only whitespace left, so not a one-liner
        source = rest
    return "{}(), {}".format(
        f.__name__,
        textwrap.dedent(source))

Demo:

>>> print open('demo.py').read()  # show source code
def sum(x, y):
    return x + y

def mean(x, y): return sum(x, y) / 2

def factorial(x):
    product = 1
    for i in xrange(1, x + 1):
        product *= i
    return product

>>> from demo import sum, mean, factorial
>>> print function_description(sum)
sum(), return x + y

>>> print function_description(mean)
mean(), return sum(x, y) / 2

>>> print function_description(factorial)
factorial(), product = 1
for i in xrange(1, x + 1):
    product *= i
return product