CODEWITHSUNDEEP
pythonstringpython-2.7liststartswith
Mr_Happy
Mr_Happy

Reputation: 39

Comparing two lists similar to startswith

I'm trying to write simple logic that will look for words in one list that start with words from other list. For example:

a = ["let","test","g"]
b = ["letter", "testing","good","egg","protest"]

should return: letter, testing, good.

I have dabbled with .startswith() but it seems to be unable to use entire list for searching. Also tried with:

if any(i in a for i in b):

but I am unable to get any results with it.

Upvotes: 0

Views: 1215

Answers (4)

mkriheli
mkriheli

Reputation: 1846

I prefer using the itertools module for such cases:

>>> [value for (start, value) in itertools.product(a,b) if value.startswith(start)]
['letter', 'testing', 'good']

Upvotes: 0

khelwood
khelwood

Reputation: 59112

If you want to find the first element in b that starts with some string, you can use next.

word = next(bword for bword in b if bword.startswith(aword))

In case there is no such word in b, you can supply a default value

word = next((bword for bword in b if bword.startswith(aword)), None)

To apply to that to each element of a, you could use a list comprehension.

words = [next((bword for bword in b if bword.startswith(aword)), None) for aword in a]

This produces:

['letter', 'testing', 'good']

Upvotes: 1

Chris_Rands
Chris_Rands

Reputation: 41168

str.startswith() accepts a tuple:

>>> a = ["let","test","g"]
>>> b = ["letter", "testing","good","egg","protest"]
>>> a = tuple(a)
>>> [item for item in b if item.startswith(a)]
['letter', 'testing', 'good']

Upvotes: 9

Chen A.
Chen A.

Reputation: 11280

You can do it with list comprehension:

>>> [y for x in a for y in b if y.startswith(x)]
['letter', 'testing', 'good']

You need to iterate over both of the lists, and then check if the elements from the list a are the start of the objects in list b.

If you just need it for conditional testing, you better off with generators. This will stop on the first match in the list:

>>> gen_exp = (y for x in a for y in b if y.startswith(x))
>>> if any(gen_exp):
        __ your logic here __

Upvotes: 4

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