# Interactive functions¶

This provides examples of uses of interactive functions, such as ginput, waitforbuttonpress and manual clabel placement.

This script must be run interactively using a backend that has a graphical user interface (for example, using GTKAgg backend, but not PS backend).

```from __future__ import print_function

import time
import matplotlib
import numpy as np
import matplotlib.cm as cm
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt

def tellme(s):
print(s)
plt.title(s, fontsize=16)
plt.draw()
```

Define a triangle by clicking three points

```plt.clf()
plt.axis([-1., 1., -1., 1.])
plt.setp(plt.gca(), autoscale_on=False)

tellme('You will define a triangle, click to begin')

plt.waitforbuttonpress()

happy = False
while not happy:
pts = []
while len(pts) < 3:
tellme('Select 3 corners with mouse')
pts = np.asarray(plt.ginput(3, timeout=-1))
if len(pts) < 3:
tellme('Too few points, starting over')
time.sleep(1)  # Wait a second

ph = plt.fill(pts[:, 0], pts[:, 1], 'r', lw=2)

tellme('Happy? Key click for yes, mouse click for no')

happy = plt.waitforbuttonpress()

# Get rid of fill
if not happy:
for p in ph:
p.remove()
```

Now contour according to distance from triangle corners - just an example

```# Define a nice function of distance from individual pts
def f(x, y, pts):
z = np.zeros_like(x)
for p in pts:
z = z + 1/(np.sqrt((x - p)**2 + (y - p)**2))
return 1/z

X, Y = np.meshgrid(np.linspace(-1, 1, 51), np.linspace(-1, 1, 51))
Z = f(X, Y, pts)

CS = plt.contour(X, Y, Z, 20)

tellme('Use mouse to select contour label locations, middle button to finish')
CL = plt.clabel(CS, manual=True)
```

Now do a zoom

```tellme('Now do a nested zoom, click to begin')
plt.waitforbuttonpress()

happy = False
while not happy:
tellme('Select two corners of zoom, middle mouse button to finish')
pts = np.asarray(plt.ginput(2, timeout=-1))

happy = len(pts) < 2
if happy:
break

pts = np.sort(pts, axis=0)
plt.axis(pts.T.ravel())

tellme('All Done!')
plt.show()
```

Gallery generated by Sphinx-Gallery