Is there a more idiomatic way to sum string lengths in Python than by using a loop?
length = 0
for string in strings:
length += len(string)
I tried sum(), but it only works for integers:
>>> sum('abc', 'de')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: sum() can't sum strings [use ''.join(seq) instead]
length = sum(len(s) for s in strings)
My first way to do it would be sum(map(len, strings)). Another way is to use a list comprehension or generator expression as the other answers have posted.
The shortest and fastest way is apply a functional programming style with map() and sum():
>>> data = ['a', 'bc', 'def', 'ghij']
>>> sum(map(len, data))
10
In Python 2, use itertools.imap instead of map for better memory performance:
>>> from itertools import imap
>>> data = ['a', 'bc', 'def', 'ghij']
>>> sum(imap(len, data))
10
I know this is an old question, but I can't help noting that the Python error message tells you how to do this:
TypeError: sum() can't sum strings [use ''.join(seq) instead]
So:
>>> strings = ['abc', 'de']
>>> print len(''.join(strings))
5
timeit module is to be believed. The answer you accepted, sum(len(s) for s in strings), is over three times as slow, and is also almost twice as slow as sum(map(len, strings)). (Speed of course doesn't matter much in Python -- if you wanted speed you'd be using Pypy, as the saying goes -- but the full generator expression is also IMO a bit of an eyesore compared to the others.)
print(sum(len(mystr) for mystr in strings))
If you care about performance use
len(''.join(strings))
else using map will suffice without sacrificing code readability or a lot of performance
sum(map(len, strings))
Although I agree with the general consensus that when using Python your first priority should not be writing efficient and scalable code, I think it would be beneficial for this post to have some timings for the proposed answers.
Using the words from the first paragraph of lorem ipsum (list of strings excluded for the sake of brevity)
In [3]: timeit("""
...: length = 0
...: for s in strings:
...: length += len(s)
...: """, globals=globals())
Out[3]: 5.197531974001322
In [4]: timeit("sum(len(s) for s in strings)", globals=globals())
Out[4]: 4.925184353021905
In [5]: timeit("sum(map(len, strings))", globals=globals())
Out[5]: 1.9876644779578783
In [6]: timeit("len(''.join(strings))", globals=globals())
Out[6]: 0.6793132669990882
So for large list of strings @Auspex is clearly to be prefered.
Here's another way using operator. Not sure if this is easier to read than the accepted answer.
import operator
length = reduce(operator.add, map(len, strings))
print length
Just to add upon ...
Adding numbers from a list stored as a string
nos = ['1','14','34']
length = sum(int(s) for s in nos)
