The number of characters in string

chars_number_sorted.py

import string
from collections import Counter, defaultdict


limited_chars = string.ascii_letters + string.digits
with open('test_1.txt') as fd:
    content = fd.read()


def func_a(s):
    ss = (x for x in s if x in limited_chars)
    c = Counter(ss)
    return c.most_common()


def func_b(s):
    res = defaultdict(int)
    for x in s:
        if x not in limited_chars:
            continue
        res[x] += 1
    return sorted(res.items(), key=lambda x: x[1], reverse=True)


def func_c(s):
    res = {}
    for x in s:
        if x not in limited_chars:
            continue
        res[x] = res[x] + 1 if x in res else 1
    return sorted(res.items(), key=lambda x: x[1], reverse=True)

[ins] In [6]: %timeit func_a(content)
1.29 ms ± 3.95 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

[nav] In [7]: %timeit func_b(content)
1.26 ms ± 28.4 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

[ins] In [8]: %timeit func_c(content)
1.39 ms ± 14.6 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

import operator
sorted(res.items(), key=operator.itemgetter(1), reverse=True)

[(k, res[k]) for k in sorted(d, key=res.get, reverse=True)]  # just a way, slower