CODEWITHSUNDEEP
pythonstringnumpy
user248237
user248237

Reputation:

checking if any element in a list starts with any of a number of prefixes in Python?

I'm trying to check if any of a number of string targets starts with one of any number of given prefixes, e.g.:

prefixes = ["a", "b", "c"]
targets = ["abar", "xbar"]

then check if any element of targets has a prefix that is in prefixes (and find those elements of targets along with the first prefix they matched). Here "abar" is the only element that fits. My own version is:

for t in target:
  if any(map(lambda x: t.startswith(x), prefixes)):
    print t

is there a better/shorter/faster way using plain Python or numpy?

Upvotes: 4

Views: 2505

Answers (4)

PaulMcG
PaulMcG

Reputation: 63749

If you want all the matches just use this list comprehension:

>>> from itertools import product
>>> matches = [(t,p) for t,p in product(targets,prefixes) if t.startswith(p)]
>>> print(matches)
[('abar', 'a'), ('cbar', 'c')]

If you just want the first one, use next with the list comprehension as a generator expression. This will short-circuit if you just want to determine if any match exists.

>>> nextmatch = next(((t,p) for t,p in product(targets,prefixes) if t.startswith(p)), None)
>>> print(nextmatch)
[('abar', 'a')]

Upvotes: 2

John La Rooy
John La Rooy

Reputation: 304355

I used lists in the result to store the prefix since there might be more than one match

>>> prefixes = ["a", "b", "c"]
>>> targets = ["abar", "xbar"]
>>> result = {t:[p for p in prefixes if t.startswith(p)] for t in targets}
>>> result
{'abar': ['a'], 'xbar': []}

If you need to filter the empty lists

>>> result = {k:v for k,v in result.items() if v}
>>> result
{'abar': ['a']}

Upvotes: 1

Yueyoum
Yueyoum

Reputation: 3073

same as @DSM

you can use filter

>>> prefixes = ("a", "b", "c")
>>> targets = ["abar", "xbar"]
>>> filter(lambda t: t.startswith(prefixes), targets)
['abar']

Upvotes: 2

martriay
martriay

Reputation: 5742

Regular expressions? Re module Python's regular expressions

Upvotes: 0

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