Python: if 'X' in 'Y' but with two similar strings as 'X'

[buran]

if you want to check string end, better use some_string.endswith(search_string). in checks for membership, so it will return True even if the search_string is in the middle of some_string. .endswith() is also recommened by PEP8 compared to using slicing.
Alternative approach is using something like

def spam():
    print('Doing something within spam()')
    
def eggs():
    print('Doing something within eggs()')
    
options = (('gifv', spam), ('gif', eggs))

some_string = 'foo.gifv'
for end, func in options:
    if some_string.endswith(end):
        func()
        break

This way it will allow to expand the list of options without ending with monstrous if/elif/elif/.../else block.
Options can be dict in python 3.7 or collections.OrderedDict (in version before that) in order to preserve the order in which will be checked