def valid_identifier(s):
    if isinstance(s, _strtypes):
        if not s or s[0].isdigit():
            return
        return s.replace(' ', '_').replace('.', '_').replace('-', '_')
    return s
Rewrite a string to be a valid identifier if it contains
dataset/ETHPy150Open blaze/blaze/blaze/expr/expressions.py/valid_identifier