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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 add_packages(packages):
 """Add external packages to the pyspark interpreter. Set the PYSPARK_SUBMIT_ARGS properly. Parameters packages: list of package names in string format """


    #if the parameter is a string, convert to a single element list
    if isinstance(packages,str):
        packages = [packages]

    _add_to_submit_args("--packages "+ ",".join(packages)  +" pyspark-shell")