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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 save_workspace(self, filename=''):
 r""" Saves all the current Projects to a 'pnm' file Parameters filename : string, optional If no filename is given, a name is genrated using the current time and date. See Notes for more information on valid file names. See Also -------- save_project Notes ----- The filename can be a string such as 'saved_file.pnm'. The string can include absolute path such as 'C:\networks\saved_file.pnm', or can be a relative path such as '..\..\saved_file.pnm', which will look 2 directories above the current working directory. It can also be a path object object such as that produced by ``pathlib`` or ``os.path`` in the Python standard library. """

        if filename == '':
            filename = 'workspace' + '_' + time.strftime('%Y%b%d_%H%M%p')
        filename = self._parse_filename(filename=filename, ext='pnm')
        d = {}
        for sim in self.values():
            d[sim.name] = sim
        with open(filename, 'wb') as f:
            pickle.dump(d, f)