如何从包含子字符串的列表中删除字符串？

Question

I have a list of strings that's structured as follows:

['3M', 'Saint Paul, Minnesota', 'A. O. Smith', 'Milwaukee, Wisconsin', 'Abbott Laboratories',...]

I want to remove the strings corresponding to cities, which all contain a comma , .

So far my code is:

for name in names:
    if '</a>' in name:
        names.remove(name)
    if re.search(', Inc.',name) != None:
        name = name.replace(',',"")
        names.append(name)
    if ',' in name:
        names.remove(name)

But I get an error ValueError: list.remove(x): x not in list at names.remove(name) .

I can't seem to understand why the 1st block, which drops if the string contains </a> works fine, but the one with commas does not.

Answer 1

You can use list comprehension to filter out invalid elements (ie the ones containing comma).

>>> l = ['3M', 'Saint Paul, Minnesota', 'A. O. Smith', 'Milwaukee, Wisconsin', 'Abbott Laboratories']
>>> result = [e for e in l if "," not in e]
>>> result
['3M', 'A. O. Smith', 'Abbott Laboratories']

Answer 2

Going off my commend about how, in Python, we generally want to "retain things we like" rather than "purge things we don't like". This is preferable because we can avoid changing the size of a list as we're iterating over it, which is never a good idea. We achieve this by filtering the original list based on a predicate ( isDesirable in this case). A predicate is a function/callable that accepts a single parameter and returns a boolean. When used in conjunction with filter , we can create an iterator that yields only those items that satisfy the condition of the predicate. We then consume the contents of that iterator to build up a new list:

names = [
    '3M',
    'Saint Paul, Minnesota',
    'A. O. Smith',
    'Milwaukee, Wisconsin',
    'Abbott Laboratories'
]

def isDesirable(name):
    return "</a>" not in name and "," not in name

print(list(filter(isDesirable, names)))

Output:

['3M', 'A. O. Smith', 'Abbott Laboratories']

However, this does not take into account the other operation you're performing: If the substring the current name contains the substring ", Inc." , we still want to retain this name, but with the comma removed.

In this situation, I would define a generator that only yields the items we want to retain. If we come across the substring ", Inc." , we modify the current name and yield it. The generator's contents are then consumed to build up a new list:

def filtered_names(names):
    for name in names:
        if ", Inc." in name:
            name = name.replace(",", "")
        if "</a>" in name or "," in name:
            continue
        yield name

print(list(filtered_names(names)))

This is by no means the only way of doing this. This is my personal preference.