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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 _varname_inj(self):
 """Customize varname for bus injections"""

        # Bus Pi
        if not self.n:
            return
        m = self.system.dae.m
        xy_idx = range(m, self.n + m)
        self.system.varname.append(
            listname='unamey',
            xy_idx=xy_idx,
            var_name='P',
            element_name=self.name)
        self.system.varname.append(
            listname='fnamey',
            xy_idx=xy_idx,
            var_name='P',
            element_name=self.name)

        # Bus Qi
        xy_idx = range(m + self.n, m + 2 * self.n)
        self.system.varname.append(
            listname='unamey',
            xy_idx=xy_idx,
            var_name='Q',
            element_name=self.name)
        self.system.varname.append(
            listname='fnamey',
            xy_idx=xy_idx,
            var_name='Q',
            element_name=self.name)