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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 _get_packages(add_pckg):
 r"""Create list of packages."""


        # Mandatory packages
        pckgs = [numpy, scipy, empymod]

        # Optional packages
        for module in [IPython, numexpr, matplotlib]:
            if module:
                pckgs += [module]

        # Cast and add add_pckg
        if add_pckg is not None:

            # Cast add_pckg
            if isinstance(add_pckg, tuple):
                add_pckg = list(add_pckg)

            if not isinstance(add_pckg, list):
                add_pckg = [add_pckg, ]

            # Add add_pckg
            pckgs += add_pckg

        return pckgs