How can I get the source code of a Python function?

Suppose I have a Python function as defined below:

def foo(arg1,arg2):
    #do something with args
    a = arg1 + arg2
    return a

I can get the name of the function using foo.func_name. How can I programmatically get its source code, as I typed above?

If the function is from a source file available on the filesystem, then inspect.getsource(foo) might be of help:

If foo is defined as:

def foo(arg1,arg2):         
    #do something with args 
    a = arg1 + arg2         
    return a  

Then:

import inspect
lines = inspect.getsource(foo)
print(lines)

Returns:

def foo(arg1,arg2):         
    #do something with args 
    a = arg1 + arg2         
    return a                

But I believe that if the function is compiled from a string, stream or imported from a compiled file, then you cannot retrieve its source code.

The inspect module has methods for retrieving source code from python objects. Seemingly it only works if the source is located in a file though. If you had that I guess you wouldn't need to get the source from the object.

The following tests inspect.getsource(foo) using Python 3.6:

import inspect

def foo(arg1,arg2):
    #do something with args
    a = arg1 + arg2
    return a

source_foo = inspect.getsource(foo)  # foo is normal function
print(source_foo)

source_max = inspect.getsource(max)  # max is a built-in function
print(source_max)

This first prints:

def foo(arg1,arg2):
    #do something with args
    a = arg1 + arg2
    return a

Then fails on inspect.getsource(max) with the following error:

TypeError: <built-in function max> is not a module, class, method, function, traceback, frame, or code object