<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_str(s):
 """Validate a string Parameters s: str Returns ------- str Raises ------ ValueError"""

    if not isinstance(s, six.string_types):
        raise ValueError("Did not found string!")
    return six.text_type(s)