def ReplaceCapitals(string):
    """
    Replaces the capital letter in a string with an underscore plus the
    corresponding lowercase character.

    **Parameters:**

    * `string`: the string to be analyzed.
    """
    newString = ''
    for char in string:
        if char.isupper():
            newString += '_%s' % char.lower()
        else:
            newString += char
    return newString
