Python remove elements from unknown list with a specific string

Question

There are similar questions to this but not quite what im looking for.

Having created a list with all files from a specific path im looking to filter out anything that does not contain a specific sequence in a string.

def filter():
    someFiles = os.listdir(somePath)
    listSize = len(someFiles)

    for i in range(0, listSize):
        if (".py" not in someFiles):
            someFiles.remove(i)
            print("{0}".format(someFiles))

Im aware i shouldn't be modifying the size of a list through a loop but i left it just to roughly give an idea of what i'm trying to accomplish

I did not make it clear, the issue that im facing is that i'm not sure what approach i should be taking when trying to remove every element that does not contain ".py". What I wrote above is more of a rough draft.

Answer 1

for i in range(0, listSize):
    if (".py" not in someFiles):
        someFiles.remove(i)

Note that you are trying to remove i from the list. i will be an index of an element in the list ( 0 , 1 , etc) and not an actual element. This will raise an error.

Simply use list comprehension to get only the files you do need:

required_files = [f for f in someFiles if '.py' in f]

You could also use filter but it will require a lambda (and also note it will return a filter object and not a list ):

required_files = list(filter(lambda x: '.py' in x, someFiles))

Answer 2

First of all, you don't need to use for loop to iterate over a list in Python. Simpler version of what you've done would be

list2 = []
for filename in list1:
    if (".py" in filename):
        list2.append(filename)

but filtering a list (or more generally, an iterator) is so common, that there is Python builtin function called, unsurprisingly, filter :

list2 = list(filter(lambda i: ".py" in i, list1))

(this would work at least in Python3)