Python计数零

Question

I have created a code which basically generates a random 20 digit number. Code below:

import random
from random import randint

n=20

def digit(n):

    range_start = 10**(n-1)
    range_end = (10**n)-1
    return randint(range_start, range_end+1)


print(digit(n))

The output of this code for example is:

49690101904335902069

Now given this code I'm just wondering how I can go about to counting the number of zeros in the output, so essentially I'm trying to create a new function called count_zero(): , but I have no idea what to put it for my parameter and what not.

Answer 1

Turn the number into a string and count the number of '0' characters:

def count_zeros(number):
    return str(number).count('0')

Demo:

>>> def count_zeros(number):
...     return str(number).count('0')
... 
>>> count_zeros(49690101904335902069)
5

Or without turning it into a string:

def count_zeros(number):
    count = 0
    while number > 9:
        count += int(number % 10 == 0)
        number //= 10
    return count

The latter approach is a lot slower however:

>>> import random
>>> import timeit
>>> test_numbers = [random.randrange(10 ** 6) for _ in xrange(1000)]
>>> def count_zeros_str(number):
...     return str(number).count('0')
... 
>>> def count_zeros_division(number):
...     count = 0
...     while number > 9:
...         count += int(number % 10 == 0)
...         number //= 10
...     return count
... 
>>> timeit.timeit('[c(n) for n in test_numbers]',
...     'from __main__ import test_numbers, count_zeros_str as c', number=5000)
2.4459421634674072
>>> timeit.timeit('[c(n) for n in test_numbers]',
...     'from __main__ import test_numbers, count_zeros_division as c', number=5000)
7.91981315612793

To combine this with your code, just add the function, and call it separately; you can pass in the result of digit() directly or store the result first, then pass it in:

print(count_zeros(digit(n)))

or separately (which allows you to show the resulting random number too):

result = digit(n)
zeros = count_zeros(result)
print('result', result, 'contains', zeros, 'zeros.')