Experiments splitter

#!/usr/bin/env python3
# Пропустить первые HEADER строк в файле и вывести следующие BODY строк.
# Повторять до готовности. Каждое BODY сохраняется в новый файл.

from sys import argv, stderr, exit

HEADER_LINES = 7
BODY_LINES = 2500
PROGRESS_STEP = 20  # print progress each N chunks
#HEADER_LINES = 1
#BODY_LINES = 3
OUTFILE_NAME = '%s-{number}.txt' % argv[1]

if len(argv) < 2:
    print('Usage: %s filename.\n'
          '  The script will split file "filename" into files %s,\n'
          '  skipping %s lines of header for each experiment\n'
          '  and writing %s lines of text.' % (argv[0], OUTFILE_NAME, HEADER_LINES, BODY_LINES))
    exit(0)

def word(count, base):
    return '%s %s%s' % (count, base, ['', 's'][count != 1])

exp_no = 0
with open(argv[1]) as inp:
    while True:
        i = -1
        for i, _ in enumerate(inp):
            if i >= HEADER_LINES - 1:
                break
        if i < HEADER_LINES - 1:
            break  # end of file reached

        exp_no += 1
        with open(OUTFILE_NAME.format(number=exp_no), 'w') as out:
            i = -1
            for i, line in enumerate(inp):
                out.write(line)
                if i >= BODY_LINES - 1:
                    break
        if i < BODY_LINES - 1:
            print('The last experiment is too short (%s only)' % word(i + 1, 'line'))
            break  # end of file reached
        if exp_no % PROGRESS_STEP == 0:
            print('%s processed' % word(exp_no, 'experiment'), file=stderr)

print('\n%s processed' % word(exp_no, 'experiment'), file=stderr)