Plot pie charts of the different timers.

        Args:
            key: Keyword used to extract data from timers.
            minfract: Don't show sections whose relative weight is less that minfract.

        Returns:
            `matplotlib` figure

def plot_pie(self, key="wall_time", minfract=0.05, **kwargs):
        """
        Plot pie charts of the different timers.

        Args:
            key: Keyword used to extract data from timers.
            minfract: Don't show sections whose relative weight is less that minfract.

        Returns:
            `matplotlib` figure
        """
        timers = self.timers()
        n = len(timers)

        # Make square figures and axes
        import matplotlib.pyplot as plt
        from matplotlib.gridspec import GridSpec
        fig = plt.gcf()
        gspec = GridSpec(n, 1)
        for idx, timer in enumerate(timers):
            ax = plt.subplot(gspec[idx, 0])
            ax.set_title(str(timer))
            timer.pie(ax=ax, key=key, minfract=minfract, show=False)

        return fig