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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 checkASN(filename):
 """ Determine if the filename provided to the function belongs to an association. Parameters filename: string Returns ------- validASN : boolean value """

    # Extract the file extn type:
    extnType = filename[filename.rfind('_')+1:filename.rfind('.')]

    # Determine if this extn name is valid for an assocation file
    if isValidAssocExtn(extnType):
        return True
    else:
        return False