semver.py

import argparse

parser = argparse.ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument('-major', action='store_true')
group.add_argument('-minor', action='store_true')
group.add_argument('-patch', action='store_true')
parser.add_argument('--file', '-f', default='VERSION')
args = parser.parse_args()

try:
    with open(args.file, 'r') as f:
        version = f.read().strip()
except FileNotFoundError:
    version = '0.0.0'

major, minor, patch = [int(x, 10) for x in version.split('.')]
if args.major:
    major += 1
    minor = 0
    patch = 0
elif args.minor:
    minor += 1
    patch = 0
elif args.patch:
    patch += 1

version = '%d.%d.%d' % (major, minor, patch)

with open(args.file, 'w') as f:
    f.write('%s\n' % version)

print(version)