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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 generate_packer_filename(provider, region, builder):
 """Generate a filename to be used by packer. Args: provider (str):
 Name of Spinnaker provider. region (str):
 Name of provider region to use. builder (str):
 Name of builder process type. Returns: str: Generated filename based on parameters. """

    filename = '{0}_{1}_{2}.json'.format(provider, region, builder)
    return filename