如果列表中未包含项目，则使用Python列表理解

Question

I have a list of strings and I'd like to find the strings that do not contain letters of a given word. I can easily find the items that do match the given word using list comprehension. I am having trouble reversing this process.

import sys

userin = sys.argv[1]
word = userin.lower()

cars = ['mercedes', 'bmw', 'ford', 'renault']

result = []
check = set(word)
result = [c for c in cars if any(l in check for l in c)]
print result

I thought this could be reversed using:

result = [c for c in cars if not(l in check for l in c)]

But that does not give the output I'm looking for. I'd be very grateful for any suggestions.

Answer 1

I think not does not do what you think it does there. What you are actually determining is as follows:

not(generator expression)

Which is the opposite of:

bool(generator expression)

The boolean value of a generator is always simply 'True' as it's a non- None python object, and they are truthy by default unless some special logic applies (such as an empty container, equaling 0 , or being the False object). Thus that part of your code simply returns False unconditionally.

What you actually meant is this:

result = [c for c in cars if not any(l in check for l in c)]

But in this case you would be better served by using set methods:

result = [c for c in cars if not check.intersection(c)]

Answer 2

To reverse I guess just use the age old if(__) == False

result = [c for c in cars if not(l in check for l in c)]

to this

result = [c for c in cars if any(l in check for l in c) == False]

Hope this helps man not too sure if thats whacha need

Edit: you can also do a not any()