Calculate N50 from list of contig sizes

calculate_N50.py

#!/usr/bin/env python3
from numpy import cumsum, argmax
from sys import stdin

def readStdin():
    ''' Read stdin line-by-line. '''
    for line in stdin:
        line = line.rstrip()
        if line == 'Exit':
            break
        yield line

def calculate_N50(contig_lengths):
    ''' Calculate contig N50. '''
    contig_lengths = sorted(contig_lengths, reverse=True)
    csum = cumsum(contig_lengths)
    N50_target_value = csum[-1] / 2
    N50_value = contig_lengths[argmax(csum >= N50_target_value)]
    return N50_value

def main():
    contig_lengths = list(map(int, readStdin()))
    print(calculate_N50(contig_lengths))


main()