Join 2 lists using zip_longest but removing groups with None

Question

How do I remove those groups which have None in them? Is there another alternative to zip_longest?

str1 = ['-', '+']
str2 = ['a','b','c']

list(itertools.zip_longest(str1, str2))

Output:

[('-','a'), ('+','b'), (None,'c')]

Expected output:

[[-a], [+b]]

Answer 1

zip_longest() is there as an alternative to the regular built-in zip(), which will truncate to the shortest list you give as an argument:

>>> str1 = ['-', '+']
>>> str2 = ['a','b','c']
>>> zipped = list(zip(str1, str2))
>>> print(zipped)
[('-', 'a'), ('+', 'b')]
>>> # the following more closely resembles your desired output
>>> condensed = [''.join(tup) for tup in zipped]
>>> print(condensed)
['-a', '+b']

Note that you can also give a keyword argument fillvalue to itertools.zip_longest() to make it fill with something besides None:

>>> zipped_long = list(itertools.zip_longest(str1, str2, fillvalue='~'))
>>> print(zipped_long)
[('-', 'a'), ('+', 'b'), ('~', 'c')]