input validation in python using Schema

input_validation.py

  schema = Schema(
        {
            'rovi_data_dir':
                And(
                    And(
                        os.path.exists,
                        os.path.isdir,
                        lambda s: os.access(s, os.R_OK),
                        error="The path to rovi data '%s' should be an existing directory and be readable. Please check" % arguments['<rovi_data_dir>']
                    ),
                    And(
                        lambda s: os.path.exists(os.path.join(os.path.realpath(s), 'bound')),
                        error="Expected the directory 'bound' to exist under the rovi data directory: '%s'. Please check!" % arguments['<rovi_data_dir>'],
                    ),
                    And(
                        lambda s: os.path.exists(os.path.join(os.path.realpath(s), 'unbound')),
                        error="Expected the directory 'unbound' to exist under the rovi data directory : '%s'. Please check!" % arguments['<rovi_data_dir>'],
                    )
                ),
            '--schema-dir':
                And(
                    And(
                        os.path.exists,
                        os.path.isdir,
                        lambda s: os.access(s, os.R_OK),
                        error="The path containing the rovi db schema sql '%s' should be an existing directory and be readable. Please check" % arguments['--schema-dir']
                    ),
                    And(
                        lambda s: os.path.exists(os.path.join(os.path.realpath(s), 'Rovi 2.0 Bound US')),
                        error="Expected the directory 'Rovi 2.0 Bound US' to exist under the schema directory: '%s'. Please check!" % arguments['--schema-dir'],
                    ),
                    And(
                        lambda s: os.path.exists(os.path.join(os.path.realpath(s), 'Rovi 2.0 Unbound')),
                        error="Expected the directory 'Rovi 2.0 Unbound' to exist under the schema directory : '%s'. Please check!" % arguments['--schema-dir'],
                    )
                ),
            '--table-load-order':
                And(
                    os.path.exists,
                    os.path.isfile,
                    error="The path to the file, '%s', doesn't exist, or doesn't point to a readable file. Please check! " % arguments['--table-load-order']
                )
        })
        
    try:
        args = schema.validate({
            '--table-load-order': arguments['--table-load-order'],
            '--schema-dir': arguments['--schema-dir'],
            'rovi_data_dir': arguments['<rovi_data_dir>']
        })

        # The '--output' directory applies only when generating the sqlite db, so
        # if sqlite != True, then don't check anything else
        if arguments['sqlite']:
            Schema(
                {
                    '--output':
                        And(
                            And(os.path.exists,
                                os.path.isdir,
                                lambda s: os.access(s, os.W_OK),
                                error="The path to the database output, '%s', doesn't exist, or doesn't point to a writeable directory. Please check! " % arguments['--output']
                            ),
                            #Or the directory should be creatable...(the existing root of the specified directory tree should be writeable)
                            And(lambda s: os.access(env.find_existing_root_dir(s), os.W_OK),
                                error="The path to the database output, '%s', has to be created, but the current process doesn't have permissions to create the directory tree. Please check!" % arguments['--output']
                            )
                        )
                }
            ).validate({'--output': arguments['--output']})

    except SchemaError as schema_error:
        exit(schema_error)