Evil Pure Python Evil

example1.py

def speak():
    print('woof')

example2.py

def speak():
    print('meow')

replace.py

import inspect
import example1 as example

def replace():
    # doesn't work because of scoping
    import example2 as example

def inspect_replace():
    current_frame = inspect.currentframe()
    # Essentially the same as 'u' in pdb
    outer_frame = current_frame.f_back
    import example2
    outer_frame.f_globals['example'] = example2
    # Have to delete any references to the frames or else they wont be
    # properly garbage collected
    del current_frame
    del outer_frame

example.speak()
replace()
example.speak()
inspect_replace()
example.speak()

Run

$ python2 replace.py 
woof
woof
meow