Passing pyplot points as arguments

Question

So I initialised a pyplot figure

import ... ## import all relevent modules

f = plt.figure(figsize=(8,3),dpi(100)
a = plt.subplot(111)
a.set_xlim(left=0,right=25,auto=False)
a.set_ylim(bottom=0,top=250,auto=False)

a.plot([5,10,15],[80,150,210])
plt.show()

This works fine... What I want to be able to do is to write a function that can update the scatter plot dynamically... Something like:

def plot_point(x_coord,y_coord):
  a.plot([x_coord],[y_coord])
  a.draw() ## I thought this would work... :(

No error, but the point doesn't get plotted. How can I get around this? The reason I've done it using figures is so I can embed it in Tkinter.

Thanks for your help!

You say "scatter plot" but you're using .plot(), not .scatter(); do you want a line that's updated or a new point on a scatter plot? — DSM
– DSM, Commented Mar 8, 2012 at 1:26
New point on a scatter plot. Let me try using scatter() not plot() — David Derry
– David Derry, Commented Mar 8, 2012 at 1:27

David Zwicker · Accepted Answer · 2012-03-08 10:35:51Z

2

plot is perfectly fine to use for plotting individual points (it is even recommend over scatter, if you don't wanna add additional information through color or size of the dots). What is missing in the initial example is setting the right linestyle; obviously, a line consisting of a single point doesn't show up. Changing the line style to '+' or something similar fixes the problem:

def plot_point(x_coord,y_coord):
  a.plot([x_coord],[y_coord], '+')

answered Mar 8, 2012 at 10:35

David Zwicker

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1 Comment

Yann Over a year ago

+1 for explaining the difference between plot and scatter and +1 (if I could) for explaining why a line of a single point doesn't display, and how to fix that...

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