Python-从列表中按前缀和后缀删除元组

Question

What's the fastest way to remove tuples from a python list (and update the list with the removed tuples) according to what the tuple starts with or ends with.

Example:

import itertools
l1 = ["a", "b", "c"]
l2 = ["d", "e", "f"]
tupl_lst = list(itertools.product(l1, l2))
tupl_lst
Out[42]: 
[('a', 'd'),
 ('a', 'e'),
 ('a', 'f'),
 ('b', 'd'),
 ('b', 'e'),
 ('b', 'f'),
 ('c', 'd'),
 ('c', 'e'),
 ('c', 'f')]

I want to remove all tuples that starts with 'a' OR ends with 'f' so that my output will look as follows:

[('b', 'd'),
 ('b', 'e'),
 ('c', 'd'),
 ('c', 'e')]

What is the fastest way to do it ?

Answer 1

You can even skip the itertools.product() and just use one list-comprehension:

l1 = ["a", "b", "c"]
l2 = ["d", "e", "f"]

tupl_lst = [(x, y) for x in l1 for y in l2 if x!="a" and y!="f"]

#output
[('b', 'd'), ('b', 'e'), ('c', 'd'), ('c', 'e')]

Answer 2

with a list comprehension:

[t for t in tupl_lst if t[0]!='a' and t[1]!='f']

with filter :

list(filter(lambda t: t[0]!='a' and t[1]!='f',tupl_lst))

Answer 3

Avoid the prefix ( a ) and suffix ( f ) altogether by iterating over slices of the lists.

[(x, y) for x in l1[1:] for y in l2[:-1]]
# [('b', 'd'), ('b', 'e'), ('c', 'd'), ('c', 'e')]