matplotlib interactive graphing (manually drawing lines on a graph)

Question

I have succesfully plotted a set of date sequenced data (X axis is date) using matplotlib. However, I want to be able to manually draw lines from one (date1, y1

Answer 1

I would write something like this:

import matplotlib.pyplot as plt
class LineDrawer(object):
    lines = []
    def draw_line(self):
        ax = plt.gca()
        xy = plt.ginput(2)

        x = [p[0] for p in xy]
        y = [p[1] for p in xy]
        line = plt.plot(x,y)
        ax.figure.canvas.draw()

        self.lines.append(line)

Using ginput() you can avoid more complicated event handling. The way it 'works' is you plot something:

plt.plot([1,2,3,4,5])
ld = LineDrawer()
ld.draw_line() # here you click on the plot

For saving/loading the line data to a file you can easily implement a method using pickle or shelve. You can also pass the necessary metadata by the method draw_line()