CLI tool to validate a Voluptuous schema (can be used as a pre-commit hook)

validate.py

#!/usr/bin/env python
# coding: utf-8
'''
Validate input file(s) against a Voluptuous schema

Pass a dash to read from stdin.
'''
from __future__ import print_function

import imp
import logging
import optparse
import sys
import yaml

try:
    from salt.utils import voluptuous as V
except ImportError:
    import voluptuous as V

try:
    from logging import NullHandler
except ImportError:
    class NullHandler(logging.Handler):
        def emit(self, record): pass

logging.basicConfig(format='%(levelname)s %(asctime)s %(module)s: %(message)s')
log = logging.getLogger(__name__)
log.addHandler(NullHandler())

VERSION = '0.1.0'

def check(schema, infile):
    data = yaml.safe_load(infile)
    return schema(data)

def get_file_contents(args):
    try:
        idx = args.index('-')
    except ValueError:
        use_stdin = False
    else:
        use_stdin = True
        args.pop(idx)

    if not sys.stdin.isatty() or use_stdin:
        stdin = sys.stdin.read()
        if stdin:
            yield stdin

    for filename in args:
        with open(filename, 'r') as f:
            yield f.read()

def process(schema_file, file_args):
    module = imp.load_source('module', schema_file)
    schema = module.schema

    for contents in get_file_contents(file_args):
        check(schema, contents)

def main():
    usage = 'Usage: %prog -s the_schema.py file1 file2'

    parser = optparse.OptionParser(
            usage=usage,
            description=__doc__,
            version=VERSION)

    parser.add_option('-s', '--schema', dest='schema',
            help='A schema to validate input file(s) against.')

    parser.add_option('-v', dest='verbose', default=0, action='count',
            help='Increment output verbosity; use multiple counts.')

    opts, args = parser.parse_args()

    log.addHandler(logging.StreamHandler())
    log.setLevel(max(logging.ERROR - (opts.verbose * 10), 1))

    if not opts.schema:
        parser.error('Schema argument is required.')

    if not args:
        parser.error('No input files given.')

    has_errors = True

    try:
        process(opts.schema, args)
    except V.MultipleInvalid as exc:
        for err in exc.errors:
            print(err, file=sys.stderr)
    except IOError as exc:
        print(exc, file=sys.stderr)
    except Exception:
        log.debug('Unhandled exception', exc_info=True)
        print('Unhandled exception. Run with -vvv flag.', file=sys.stderr)
    else:
        has_errors = False

    return has_errors

if __name__ == '__main__':
    raise SystemExit(main())