Cdtjkyj

A variation on @Primusa answer without using update:

from collections import Counter



words = ["tree", "bone", "indigo", "developer"]

counts = Counter(c for word in words for c in set(word.lower()) if c.isalpha())

Output

Counter({'e': 3, 'o': 3, 'r': 2, 'd': 2, 'n': 2, 'p': 1, 'i': 1, 'b': 1, 'v': 1, 'g': 1, 'l': 1, 't': 1})

Basically convert each word to a set and then iterate over each set.

Create a counter object and then update it with sets for each word:

from collections import Counter

c = Counter()



for word in wordlist:

    c.update(set(word.lower()))

One without Counter

words=["tree","bone","indigo","developer"]

d={}

for word in words:         # iterate over words

    for i in set(word):    # to remove the duplication of characters within word

        d[i]=d.get(i,0)+1

Output

{'b': 1,

 'd': 2,

 'e': 3,

 'g': 1,

 'i': 1,

 'l': 1,

 'n': 2,

 'o': 3,

 'p': 1,

 'r': 2,

 't': 1,

 'v': 1}

Comparing speed of the solutions presented so far:

def f1(words):

    c = Counter()

    for word in words:

        c.update(set(word.lower()))

    return c



def f2(words):

    return Counter(

        c

        for word in words

        for c in set(word.lower()))



def f3(words):

    d = {}

    for word in words:

        for i in set(word.lower()):

            d[i] = d.get(i, 0) + 1

    return d

My timing function (using different sizes for the list of words):

word_list = [

    'tree', 'bone', 'indigo', 'developer', 'python',

    'language', 'timeit', 'xerox', 'printer', 'offset',

]



for exp in range(5):

    words = word_list * 10**exp



    result_list = 

    for i in range(1, 4):

        t = timeit.timeit(

            'f(words)',

            'from __main__ import words,  f{} as f'.format(i),

            number=100)

        result_list.append((i, t))



    print('{:10,d} words | {}'.format(

        len(words),

        ' | '.join(

            'f{} {:8.4f} sec'.format(i, t) for i, t in result_list)))

The results:

        10 words | f1   0.0028 sec | f2   0.0012 sec | f3   0.0011 sec

       100 words | f1   0.0245 sec | f2   0.0082 sec | f3   0.0113 sec

     1,000 words | f1   0.2450 sec | f2   0.0812 sec | f3   0.1134 sec

    10,000 words | f1   2.4601 sec | f2   0.8113 sec | f3   1.1335 sec

   100,000 words | f1  24.4195 sec | f2   8.1828 sec | f3  11.2167 sec

The Counter with list comprehension (here as f2()) seems to be the fastest. Using counter.update() seems to be a slow point (here as f1()).

The other solutions are good, but they specifically don't include the letters with zero frequency. Here's an approach which does, but is approximately 2-3 times slower than the others.

import string

counts = {c: len([w for w in words if c in w.lower()]) for c in string.ascii_lowercase}

which produces a dict like this:

{'a': 4, 'b': 2, 'c': 2, 'd': 4, 'e': 7, 'f': 2, 'g': 2, 'h': 3, 'i': 7, 'j': 0, 'k': 0, 'l': 4, 'm': 5, 'n': 4, 'o': 4, 'p': 1, 'q': 0, 'r': 5, 's': 3, 't': 3, 'u': 2, 'v': 0, 'w': 3, 'x': 0, 'y': 2, 'z': 1}

Here's my update of Ralf's timings:

        10 words | f1   0.0004 sec | f2   0.0004 sec | f3   0.0003 sec | f4   0.0010 sec

       100 words | f1   0.0019 sec | f2   0.0014 sec | f3   0.0013 sec | f4   0.0034 sec

     1,000 words | f1   0.0180 sec | f2   0.0118 sec | f3   0.0140 sec | f4   0.0298 sec

    10,000 words | f1   0.1960 sec | f2   0.1278 sec | f3   0.1542 sec | f4   0.2648 sec

   100,000 words | f1   2.0859 sec | f2   1.3971 sec | f3   1.6815 sec | f4   3.5196 sec

based on the following code and the word list from https://github.com/dwyl/english-words/

import string

import timeit

import random

from collections import Counter



def f1(words):

    c = Counter()

    for word in words:

        c.update(set(word.lower()))

    return c



def f2(words):

    return Counter(

        c

        for word in words

        for c in set(word.lower()))



def f3(words):

    d = {}

    for word in words:

        for i in set(word.lower()):

            d[i] = d.get(i, 0) + 1

    return d





def f4(words):

    d = {c: len([w for w in words if c in w.lower()]) for c in string.ascii_lowercase} 

    return d





with open('words.txt') as word_file:

    valid_words = set(word_file.read().split())



for exp in range(5):



    result_list = 

    for i in range(1, 5):

        t = timeit.timeit(

            'f(words)',

            'from __main__ import f{} as f, valid_words, exp; import random; words = random.sample(valid_words, 10**exp)'.format(i),

            number=100)

        result_list.append((i, t))



    print('{:10,d} words | {}'.format(

        len(words),

        ' | '.join(

            'f{} {:8.4f} sec'.format(i, t) for i, t in result_list)))



print(f4(random.sample(valid_words, 10000)))

print(f4(random.sample(valid_words, 1000)))

print(f4(random.sample(valid_words, 100)))

print(f4(random.sample(valid_words, 10)))