Pythonic way to redefine function? (Flake8 F811 error)

Question

I'm trying to write a downloader wrapper module in python that may use pycurl, selenium or the good-ol' requests to download a URL, along the lines of

# import pycurl inside a try-except block, logging errors
# also import selenium stuff inside a try-except block logging errors
# then
def pycurl_downloader(*args, **kwargs):
    raise NotImplementedError

if 'pycurl' in sys.modules:
    def pycurl_downloader(url, char_encoding=None):
        # actual implementation, now we are certain pycurl is there

# similar for selenium

then when a site doesn't make use of silly DOM-modifying JavaScript I could just use pycurl (or if it isn't found, fallback to requests gracefully), otherwise use the various selenium drivers (again with graceful fallback if a driver fails).

But flake8 complains of an F811 redefinition error (redefining pycurl_downloader and also selenium_downloader later too) in the code above.

I could try to use some _not_implemented_function dummy and assign the name pycurl_downloader to this, then write the _real_pycurl_downloader function and reassign:

pycurl_downloader = _not_implemented_func
if 'pycurl' in sys.modules:
    def _real_pycurl_downloader(...):
        # blah
    pycurl_downloader = _real_pycurl_downloader

but that doesn't feel right. Does anyone have a better idea?

Answer 1

Using if-else to only define the function once should shut flake8 up:

if 'pycurl' in sys.modules:
    def pycurl_downloader(url, char_encoding=None):
        # actual implementation, now we are certain pycurl is there
        ...
else:
    def pycurl_downloader(*args, **kwargs):
        raise NotImplementedError