字符串Python列表中没有项目

Question

I have a list of things I want to filter out of a csv, and I'm trying to figure out a pythonic way to do it. EG, this is what I'm doing:

with open('output.csv', 'wb') as outf:
    with open('input.csv', 'rbU') as inf:
         read = csv.reader(inf)
         outwriter = csv.writer(outf)
         notstrings = ['and', 'or', '&', 'is', 'a', 'the']
         for row in read:
             (if none of notstrings in row[3])
                 outwriter(row)

I don't know what to put in the parentheses (or if there's a better overall way to go about this).

Answer 1

You can use the any() function to test each of the words in your list against a column:

if not any(w in row[3] for w in notstrings):
    # none of the strings are found, write the row

This will be true if none of those strings appear in row[3] . It'll match substrings , however, so false-positive would be a match for 'a' in 'false-positive for example.

Put into context:

with open('output.csv', 'wb') as outf:
    with open('input.csv', 'rbU') as inf:
        read = csv.reader(inf)
        outwriter = csv.writer(outf)
        notstrings = ['and', 'or', '&', 'is', 'a', 'the']
        for row in read:
            if not any(w in row[3] for w in notstrings):
                outwriter(row)

If you need to honour word boundaries then a regular expression is going to be a better idea here:

notstrings = re.compile(r'(?:\b(?:and|or|is|a|the)\b)|(?:\B&\B)')
if not notstrings.search(row[3]):
    # none of the words are found, write the row

I created a Regex101 demo for the expression to demonstrate how it works. It has two branches:

• \\b(?:and|or|is|a|the)\\b - matches any of the words in the list provided they are at the start, end, or between non-word characters (punctuation, whitespace, etc.)
• \\B&\\B - matches the & character if at the start, end, or between non-word characters. You can't use \\b here as & is itself not a word character.

Answer 2

You can use sets. In this code, I transform your list into a set. I transform your row[3] into a set of words and I check the intersection between the two sets. If there is not intersection, that means none of the words in notstrings are in row[3] .

Using sets, you make sure that you match only words and not parts of words.

with open('output.csv', 'wb') as outf:
    with open('input.csv', 'rbU') as inf:
        read = csv.reader(inf)
        outwriter = csv.writer(outf)
        notstrings = set(['and', 'or', '&', 'is', 'a', 'the'])
        for row in read:
            if not notstrings.intersection(set(row[3].split(' '))):
                outwriter(row)