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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def makeFeaClassName(name, existingClassNames=None):
 """Make a glyph class name which is legal to use in feature text. Ensures the name only includes characters in "A-Za-z0-9._", and isn't already defined. """

    name = re.sub(r"[^A-Za-z0-9._]", r"", name)
    if existingClassNames is None:
        return name
    i = 1
    origName = name
    while name in existingClassNames:
        name = "%s_%d" % (origName, i)
        i += 1
    return name