Drawing obtuse circular arc with arrowhead in matplotlib
Question: I am new to Python, though I do have previous programming experience. My
current interest is to generate good quality schematics (and maybe later on
also data graphs).

I need to draw a circlar arc with an arrowhead at the end point. I have sieved
through many posts and tried my hand at a few examples, but it seems I still
miss some basic knowledge. So I need something like this:

<http://i.stack.imgur.com/Z5V86.png>

I was experimenting with the example below, trying to initially plot a
circular arc, but even this does not work. I am using matplotlib.patches but I
am open to other suggestions for what I need.

    
    
    # -*- coding: utf-8 -*-
    import numpy as np
    import matplotlib.pyplot as plt
    from matplotlib.patches import Ellipse, Arc
    from matplotlib import cm, colors, patches
    from math import pi
    
    fig = plt.figure()
    ax = fig.add_subplot(1,1,1)
    ellipse = Arc([2.5,2.5],1,1,0,0,pi,color='green', linewidth='0.5')
    ax.add_patch(ellipse)
    plt.show()
    


Answer: Well,

  * if you want an angle of `pi`, pass `180`. 
  * linewidth must be a scalar. pass `.5` and not `'.5'` as linewidth parameter
  * you need to change the limits of the axes, or you want see the arc. Add something like `ax.set_xlim(1.5,3.1)` and `ax.set_ylim(2.4,3.7)`.

You may also want to opt for another strategy, something like

`ax.plot([.5],[.5],marker=r'$\circlearrowleft$',ms=100)`

