How to count members of a set in a string in Python?

Question

I have a list of letters and letter clusters, like this:

['x', 'str', 'a', 'pr']

I have a string that I need to know how many total occurrences of any member of the list are in it:

stripe = 1, rope = 0,, rprpraxp = 4, etc

Now I can loop over the members of the list counting occurrences of each member and then total them, like this:

sublist = ['x', 'str', 'a', 'pr']
string = "rprpraxp"
inst = 0
for member in sublist:
    inst = inst + string.count(member)
print(inst)

However I am wondering if I am missing a shorter, simpler, more intuitive and more Pythonic way of counting the members of a set of items in another string, something like:

inst = string.multicount(['x', 'str', 'a', 'pr'])

Anything like this exist?

Thanks.

What if strings overlap? Example: list is ['ab', 'ba'] and string is 'aba'. Is the answer 1 or 2? — trincot
– trincot, Commented Nov 3, 2017 at 18:42
I'm coding my text to make sure that does not happen - but good catch! — Sindyr
– Sindyr, Commented Nov 3, 2017 at 19:52

scharette · Accepted Answer · 2017-11-03 18:53:55Z

2

I would use map and sum:

sublist = ['x', 'str', 'a', 'pr']
string = "rprpraxp"
print(sum(map(string.count, sublist)))

edited Nov 3, 2017 at 18:53

answered Nov 3, 2017 at 18:41

scharette

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4 Comments

Sindyr Over a year ago

Because sets are faster?

scharette Over a year ago

Yes, sets have faster lookups than list. You won't notice any difference in this case because it is a small list of strings. I'm just pointing it out. I edited to let it as a list though it is completely trivial in this case.

Sindyr Over a year ago

Just to confirm, what you are calling a set is the same thing as a tuple, right? Or is this a new type I haven't bumped into yet?

scharette Over a year ago

Yea Initially I used tuples and it was my mistake. I understand the confusion. here is the way your create both mytuple = (1,2,3) and myset = {1,2,3}. Set can also be initialize like this myset=set(1,2,3)

Ignacio Vazquez-Abrams · Accepted Answer · 2017-11-03 18:41:38Z

0

>>> S = "rprpraxp"
>>> L = ['x', 'str', 'a', 'pr']
>>> sum(S.count(e) for e in L if e in S)
4

answered Nov 3, 2017 at 18:41

Ignacio Vazquez-Abrams

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2 Comments

Robᵩ Over a year ago

Won't you get the same answer if you omit if e in S?

Ignacio Vazquez-Abrams Over a year ago

@Robᵩ: Sure. Might even be a bit faster.

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