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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 popup(self, title, callfn, initialdir=None, filename=None):
 """Let user select and load file."""

        self.cb = callfn
        self.filew.set_title(title)
        if initialdir:
            self.filew.set_current_folder(initialdir)

        if filename:
            #self.filew.set_filename(filename)
            self.filew.set_current_name(filename)

        self.filew.show()