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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_initial_sync_op(self):
 """ Get the op to copy-initialized all local variables from PS. """

        def strip_port(s):
            if s.endswith(':0'):
                return s[:-2]
            return s
        local_vars = tf.local_variables()
        local_var_by_name = dict([(strip_port(v.name), v) for v in local_vars])
        ops = []
        nr_shadow_vars = len(self._shadow_vars)
        for v in self._shadow_vars:
            vname = strip_port(v.name)
            for i in range(self.nr_gpu):
                name = 'tower%s/%s' % (i, vname)
                assert name in local_var_by_name, \
                    "Shadow variable {} doesn't match a corresponding local variable!".format(v.name)
                copy_to = local_var_by_name[name]
                # logger.info("{} -> {}".format(v.name, copy_to.name))
                ops.append(copy_to.assign(v.read_value()))
        return tf.group(*ops, name='sync_{}_variables_from_ps'.format(nr_shadow_vars))