Finding Multiple Occurrences of a String Within a String in Python

Finding multiple occurrences of a string within a string in Python

Using regular expressions, you can use re.finditer to find all (non-overlapping) occurences:

>>> import re
>>> text = 'Allowed Hello Hollow'
>>> for m in re.finditer('ll', text):
         print('ll found', m.start(), m.end())

ll found 1 3
ll found 10 12
ll found 16 18

Alternatively, if you don't want the overhead of regular expressions, you can also repeatedly use str.find to get the next index:

>>> text = 'Allowed Hello Hollow'
>>> index = 0
>>> while index < len(text):
        index = text.find('ll', index)
        if index == -1:
            break
        print('ll found at', index)
        index += 2 # +2 because len('ll') == 2

ll found at  1
ll found at  10
ll found at  16

This also works for lists and other sequences.

How to find all occurrences of a substring?

There is no simple built-in string function that does what you're looking for, but you could use the more powerful regular expressions:

import re
[m.start() for m in re.finditer('test', 'test test test test')]
#[0, 5, 10, 15]

If you want to find overlapping matches, lookahead will do that:

[m.start() for m in re.finditer('(?=tt)', 'ttt')]
#[0, 1]

If you want a reverse find-all without overlaps, you can combine positive and negative lookahead into an expression like this:

search = 'tt'
[m.start() for m in re.finditer('(?=%s)(?!.{1,%d}%s)' % (search, len(search)-1, search), 'ttt')]
#[1]

re.finditer returns a generator, so you could change the [] in the above to () to get a generator instead of a list which will be more efficient if you're only iterating through the results once.

Check if multiple strings exist in another string

You can use any:

a_string = "A string is more than its parts!"
matches = ["more", "wholesome", "milk"]

if any(x in a_string for x in matches):

Similarly to check if all the strings from the list are found, use all instead of any.

How do I check whether or not a substring appears multiple times within a list in Python?

You can use in for each string in the list:

>>> player_hand = ['Ace of Spades', 'Nine of Diamonds', 'Ace of Diamonds']
>>> sum(1 for x in player_hand if 'Ace' in x)
2

This uses a generator expression to go through the list that gives you a 1 if Ace is in a string of the list. Summing up the ones gives you the total count of strings that contain Ace.

Find all occurrences of a character in a String

One way to do this is to find the indices using list comprehension:

currentWord = "hello"

guess = "l"

occurrences = currentWord.count(guess)

indices = [i for i, a in enumerate(currentWord) if a == guess]

print indices

output:

[2, 3]

Finding a string multiple times in another String - Python

You can do:

>>> haystack = "abcdefabc. asdli! ndsf acba saa abe?"
>>> needle = "abc"
>>> for i, _ in enumerate(haystack):
...     if haystack[i:i + len(needle)] == needle:
...         print (i)
...
0
6

find multiple string occurrences in Python

You could do:

if all( x in 'hello world' for x in ['hel','ell','orl'] ):
    print "Found all of them"

The built-in functions all and any are useful for this kind of thing.

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