Plus Minus in Python

You're given an array containing integer values. You need to print the
fraction of count of positive numbers, negative numbers and zeroes to
the total numbers. Print the value of the fractions correct to 3
decimal places.


Input Format


First line contains \$N\$, which is the size of the array. Next line
contains \$N\$ integers \$A_1, A_2, A_3, ⋯, A_N\$, separated by spaces.


Constraints

• \$1 \le N \le 100\$

• \$−100 \le A_{i} \le 100\$

Solution

from __future__ import division

N = int(raw_input())
ary = map(int, raw_input().split())

count_negatives = len(filter(lambda x: x 0, ary))
count_zeros = len(filter(lambda x: x == 0, ary))

print count_positives / N
print count_negatives / N
print count_zeros / N

It seems that this problem has a very straightforward solution but I am more interested if there is a better functional approach.

Print the value of the fractions correct to 3 decimal places.

You didn't really do this part. You're just printing the full float. You can use str.format() to print to three places. With this syntax:

print "{:.3f}".format(count_positives / N)

The .3f syntax tells Python to print the first three digits only. Note that str.format will actually round the value, not just truncate it:

"{:.3f}".format(1.3449)
>>> '1.345'

Though, since you're just printing the value by itself, you can use the format builtin where you pass the string and the format as a string.

format(count_positives / N, '.3f')

You don't need a filter to count the zeros. Lists have a built in count function which will return the number of times a particular object occurs in it. Like this:

count_zeros = ary.count(0)

StackExchange Code Review Q#105337, answer score: 7