How to see if a string contains all substrings from a list? [Python]

Question

Here's the scenario:

I have a long list of time-stamped file names with characters before and after the time-stamp.

Something like this: prefix_20160817_suffix

What I want is a list (which will ultimately be a subset of the original list) that contains file names with specific prefixes, suffixes, and parts of the timestamp. These specific strings are already given in a list. Note: this "contains" list might vary in size.

For example: ['prefix1', '2016', 'suffix'] or ['201608', 'suffix']

How can I easily get a list of file names that contain every element in the "contains" array?

Here's some pseudo code to demonstrate what I want:

for each fileName in the master list:
    if the fileName contains EVERY element in the "contains" array:
        add fileName to filtered list of filenames

filtered_list = [fn for fn in master_list if all(item in fn for item in contains_list)] — Steven Rumbalski
– Steven Rumbalski, Commented Aug 17, 2016 at 17:04
Out of curiosity, why the downvote? What should I have done differently? — Luke H
– Luke H, Commented Aug 17, 2016 at 17:16

Martijn Pieters · Accepted Answer · 2016-08-17 17:03:46Z

6

I'd compile the list into a fnmatch pattern:

import fnmatch

pattern = '*'.join(contains)
filetered_filenames = fnmatch.filter(master_list, pattern)

This basically concatenates all strings in contains into a glob pattern with * wildcards in between. This assumes the order of contains is significant. Given that you are looking for prefixes, suffixes and (parts of) dates in between, that's not that much of a stretch.

It is important to note that if you run this on an OS that has a case-insensitive filesystem, that fnmatch matching is also case-insensitive. This is usually exactly what you'd want in that case.

answered Aug 17, 2016 at 17:03

Martijn Pieters

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2 Comments

Luke H Over a year ago

Thanks, this is an awesome answer. I can get my "contains" array as a string with asterisks VIA user input so it is even smoother this way.

Martijn Pieters Over a year ago

@LukeH: if you are applying this to os.lisdir() output you may want to check out the glob module too and skip having to calling os.listdir() yourself.

Graham · Accepted Answer · 2017-09-27 04:34:20Z

5

You're looking for something like that (using list comprehension and all():

>>> files = ["prefix_20160817_suffix", "some_other_file_with_suffix"]
>>> contains = ['prefix', '2016', 'suffix']
>>> [ f for f in files if all(c in f for c in contains) ]
['prefix_20160817_suffix']

edited Sep 27, 2017 at 4:34

Graham

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answered Aug 17, 2016 at 17:06

Ohad Eytan

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Comments

dawg · Accepted Answer · 2016-08-17 17:14:03Z

Given:

>>> cond1=['prefix1', '2016', 'suffix']
>>> cond2=['201608', 'suffix']
>>> fn="prefix_20160817_suffix"

You can test the existence of each substring in the list of conditions with in and (in the interim example) a list comprehension:

>>> [e in fn for e in cond1]
[False, True, True]
>>> [e in fn for e in cond2]
[True, True]

That can then be used in a single all statement to test all the substrings:

>>> all(e in fn for e in cond1)
False
>>> all(e in fn for e in cond2)
True

Then you can combine with filter (or use a list comprehension or a loop) to filter the list:

>>> fns=["prefix_20160817_suffix", "prefix1_20160817_suffix"]
>>> filter(lambda fn: all(e in fn for e in cond1), fns)
['prefix1_20160817_suffix']
>>> filter(lambda fn: all(e in fn for e in cond2), fns)
['prefix_20160817_suffix', 'prefix1_20160817_suffix']

janbrohl · Accepted Answer · 2016-08-17 17:13:06Z

1

Your pseudocode was not far from a usable implementation as you see:

masterList=["prefix_20160817_suffix"]
containsArray=['prefix1', '2016', 'suffix']
filteredListOfFilenames=[]

for fileName in masterList:
    if all((element in fileName) for element in containsArray):
        filteredListOfFilenames.append(fileName)

I would suggest to have a deeper look into the really good official tutorial - it contains many useful things.

answered Aug 17, 2016 at 17:13

janbrohl

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Comments

A Magoon · Accepted Answer · 2016-08-17 17:09:46Z

0

This should work for you.

filtered_list = []

for file_name in master_list:
    for element in contains_array:
        if element not in file_name:
            break
        filtered_list.append(file_name)

answered Aug 17, 2016 at 17:09

A Magoon

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