Automatically add figure labels (a), (b), (c), etc. to axes. Labels are located at the top-left of the axis, at the same horizontal position as the y-label.

add_labels.py

def add_labels(axes, style=r'(%s)'):
    """
    Adds figure labels (a), (b), (c), etc. to axes.
    Must be called after plt.tight_layout().
    """

    alphabet = 'abcdefghijkl'
    labels = [style % letter for letter in alphabet]

    # EXTREME hack alert.
    # For some magical reason, this is necessary to get the bounding boxes correct.
    axes[0].figure.savefig("/tmp/hallo.pdf")   

    for i, ax in enumerate(axes):
        transform = ax.transAxes
        inv_transform = ax.transAxes.inverted()
        ylabelbox = ax.yaxis.label.get_window_extent()
        axbox = ax.get_window_extent()
        labelx_pixel = ylabelbox.x0
        labely_pixel = axbox.y1
        labelx, labely = inv_transform.transform((labelx_pixel, labely_pixel))
        ax.text(labelx, labely, labels[i], transform=transform, va='top', ha='left')