Generate string for email address login with defined length and
        alphabet.

        :param min_length: (optional) min login length.
        Default value is ``6``.
        :param max_length: (optional) max login length.
        Default value is ``10``.
        :param digits: (optional) use digits in login generation.
        Default value is ``True``.

def generate_login(self, min_length=6, max_length=10, digits=True):
        """
        Generate string for email address login with defined length and
        alphabet.

        :param min_length: (optional) min login length.
        Default value is ``6``.
        :param max_length: (optional) max login length.
        Default value is ``10``.
        :param digits: (optional) use digits in login generation.
        Default value is ``True``.
        """
        chars = string.ascii_lowercase
        if digits:
            chars += string.digits
        length = random.randint(min_length, max_length)
        return ''.join(random.choice(chars) for x in range(length))