gist for working on annotation range function

annotate_range.py

def add_range_annotation(ax, start, end, txt_str, y_height=.5, txt_kwargs=None, arrow_kwargs=None):
    """
    Adds horizontal arrow annotation with text in the middle

    Parameters
    ----------
    ax : matplotlib.Axes
        The axes to draw to

    start : float
        start of line

    end : float
        end of line

    txt_str : string
        The text to add

    y_height : float
        The height of the line

    txt_kwargs : dict or None
        Extra kwargs to pass to the text

    arrow_kwargs : dict or None
        Extra kwargs to pass to the annotate

    Returns
    -------
    tuple
        (annotation, text)
    """

    if txt_kwargs is None:
        txt_kwargs = {}
    if arrow_kwargs is None:
        # default to your arrowprops
        arrow_kwargs = {'arrowprops':dict(arrowstyle="<->",
                            connectionstyle="bar",
                            ec="k",
                            shrinkA=5, shrinkB=5,
                            )}

    trans = ax.get_xaxis_transform()

    ann = ax.annotate('', xy=(start, y_height),
                        xytext=(end, y_height),
                        transform=trans,
                        **arrow_kwargs)
    txt = ax.text((start + end) / 2,
                  y_height + .05,
                  txt_str,
                  **txt_kwargs)


    if plt.isinteractive():
        plt.draw()
    return ann, txt

Here are some suggestions:

• Allow for arbitrary rotation (easily done with a start and end points getting their own xy coordinates)
• Other shapes besides square brackets. I tried doing this by changing connectionstyle, but that didn't work. Could be done by using two arrows instead of one connected arrow, but might require too much of a retool.
• Center the text by default
• Perhaps a value that allows you to vary the hight of the bracket? I.e., allows you to set the distance between the tip of the arrows and the bar connecting them?

I have other suggestions, but they start to bloat what is probably better off a one trick pony. Let me know if you'd like to hear them too.

@arijun hearing them is good, implementations are better ;)

and I think if you pass in different arrowprops into arrow_kwargs you can do some of what you want.