def match_unischema_fields(schema, field_regex):
    """Returns a list of :class:`~petastorm.unischema.UnischemaField` objects that match a regular expression.

    :param schema: An instance of a :class:`~petastorm.unischema.Unischema` object.
    :param field_regex: A list of regular expression patterns. A field is matched if the regular expression matches
      the entire field name.
    :return: A list of :class:`~petastorm.unischema.UnischemaField` instances matching at least one of the regular
      expression patterns given by ``field_regex``.
    """
    if field_regex:
        unischema_fields = set()
        legacy_unischema_fields = set()
        for pattern in field_regex:
            unischema_fields |= {field for field_name, field in schema.fields.items() if
                                 _fullmatch(pattern, field_name)}
            legacy_unischema_fields |= {field for field_name, field in schema.fields.items()
                                        if re.match(pattern, field_name)}
        if unischema_fields != legacy_unischema_fields:
            field_names = {f.name for f in unischema_fields}
            legacy_field_names = {f.name for f in legacy_unischema_fields}
            # Sorting list of diff_names so it's easier to unit-test the message
            diff_names = sorted(list((field_names | legacy_field_names) - (field_names & legacy_field_names)))
            warnings.warn('schema_fields behavior has changed. Now, regular expression pattern must match'
                          ' the entire field name. The change in the behavior affects '
                          'the following fields: {}'.format(', '.join(diff_names)))
        return list(unischema_fields)
    else:
        return []
Returns a list of :class:`~petastorm.unischema.UnischemaField` objects that match a regular expression.

    :param schema: An instance of a :class:`~petastorm.unischema.Unischema` object.
    :param field_regex: A list of regular expression patterns. A field is matched if the regular expression matches
      the entire field name.
    :return: A list of :class:`~petastorm.unischema.UnischemaField` instances matching at least one of the regular
      expression patterns given by ``field_regex``.
    
petastorm/unischema.py