<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _normalize_helper(number, replacements, remove_non_matches):
 """Normalizes a string of characters representing a phone number by replacing all characters found in the accompanying map with the values therein, and stripping all other characters if remove_non_matches is true. Arguments: number -- a string representing a phone number replacements -- a mapping of characters to what they should be replaced by in the normalized version of the phone number remove_non_matches -- indicates whether characters that are not able to be replaced should be stripped from the number. If this is False, they will be left unchanged in the number. Returns the normalized string version of the phone number. """

    normalized_number = []
    for char in number:
        new_digit = replacements.get(char.upper(), None)
        if new_digit is not None:
            normalized_number.append(new_digit)
        elif not remove_non_matches:
            normalized_number.append(char)
        # If neither of the above are true, we remove this character
    return U_EMPTY_STRING.join(normalized_number)