Python: Finding a substring within a string from a list, but saving the substring

Let's look at this example:

s = "Thisisarandomstringthatiwanttotype"
subst = ["This", "random", "hullo", "type"]

To return all the substrings that match:

filter(lambda x: x in s, subs)
>> ['This', 'random', 'type']

To return the starting index of the substrings that match, you can pass the list of strings returned from the code segment above to a map function to find their index:

map(lambda x: s.index(x), filter(lambda x: x in s, subs))
>> [0, 7, 30]

Similarly, you could check the length of the returned strings using map over the filter:

map(lambda x: len(x), filter(lambda x: x in s, subs))
>> [4, 6, 4]

Or find the length of the longest substring returned:

max(filter(lambda x: x in s, subst), key=len)
>> 'random'

There are multiple ways to do this. Regular expressions (As FreddieV4 suggested) are very powerful.

However another simple approach is using a list comprehension like:

matches = [x for x in string.split() if x in substrings]

Which will loop over the the words in the string and check if the word fits one of the substrings, if so it will be returned and hence can be used for logging purposes.

You can even further extend this to handle a list of strings as input instead of a single string - all in a single list comprehension.

An extensive example is shown below:

substrings = ["cool","test","notpresent"]

#get matches for a single string
string = "This is a basic test"
matches = [x for x in string.split() if x in substrings]
print(matches)
# >> ['test']


#get matches for multiple strings
strings = ["I am so awesome", "you are cool", "I think so", "Yep this is a test"]
matches = [x for string in strings for x in string.split() if x in substrings]
print(matches)
# >> ['cool', 'test']

For this sort of thing, you could use the re module.

>>> import re
>>> m = re.search(r"substring1, substring2, substring3", string)

string would be the string you're searching through, and m would be the variable that contains the group of strings matching whatever substrings you're looking for i.e. substring1, substring2, substring3; you could use RegEx patterns rather than substrings as well.