1. Numpy, pylab, matplotlib (follow-up)
Professor Hugh C. Lauer CS-1004 — Introduction to Programming for Non-Majors
(Slides include materials from Python Programming: An Introduction to Computer Science, 2nd edition, by John Zelle and copyright notes by Prof. George Heineman of Worcester Polytechnic Institute)
CS-1004, A-Term 2014
Numpy, pylab, matplotlib

2. Follow-up from Prof. Heineman
Lecture notes from Friday are here:–
Link also on course website (under Lecture Notes)
Useful stuff at end of notes, beyond what he covered in lecture
Read especially, §1.7, §1.8
Try the “Debugging Challenge” §1.8
Questions on quizzes like this
CS-2301, D-Term 2014
Introduction

3. Follow-up from Prof. Heineman (continued)
Pylab
Another way of accessing matplotlib
I.e., a .py script:–
from matplotlib.pylab import * import matplotlib.pylab __doc__ = matplotlib.pylab.__doc__
matplotlib.pylab is a longer script
Containing
# provide the recommended moduleabbrevs in # the pylab namespace
import matplotlib.pyplot as plt
import numpy as np
import numpy.ma as ma
Is anyone still having trouble installing matplotlib?
CS-2301, D-Term 2014
Introduction

4. Follow-up from Prof. Heineman — numpy
Principal class is ‘array’
Somewhat like lists but,
Multiple dimensions
Different way of indexing 2nd and subsequent dimensions
More efficient internally
Tutorial:
Check it out
Much will be over your head now
More useful after end of course
CS-2301, D-Term 2014
Introduction

5. Numpy and arrays — Example
L = [1, 2, 3, 4, 5] M = [] N = [] P = []
for x in L: M.append(x*x) N.append(sqrt(x)) P.append(2**x)
Q = [L, M, N, P] Q1 = numpy.array(Q)
With Python lists
Q[2][3]
With numpy arrays
Q1[2, 3]
CS-2301, D-Term 2014
Introduction

6. Questions?
CS-2301, D-Term 2014
Introduction

7. Follow-up from Prof. Heineman — “Compile often!”
What does this mean?
Especially since Python is an interpretive language?
Example:– typing code into Python shell
Errors show up (almost) immediately
Example:– typing into a module
When do errors show up?
What does “Run module” menu command do?
Resets shell
(Virtually) “types” content of module into shell
As if you typed it yourself!
Picks up some errors …
… as interpreter
But some errors cannot be caught until you actually call the function!
CS-2301, D-Term 2014
Introduction

8. Additional advice — “Test often”
Example 1 — Homework #2
Q3 asks you to print out information for each term
Why?
Answer:– so you can see that it is working correctly!
How many had it working the first time you tried it?
Q6 asks you to use the function you developed in Q3 100 times (or more)
What about all those lines of debug output?
Options:–
Comment out the print lines
Copy Q3 function to Q6 function with new name
Remove or comment out print lines
Write a separate test program or function
CS-2301, D-Term 2014
Introduction

9. Example — Pong Separate into two parts Physics part:–
Physics of the motion
Display in window
Physics part:–
Motion in each dimension is independent of other dimension
Function:– move1D(pos, vel, uBound, lBound)
Returns new positions, accounting for bouncing off edges
Testing physics part:–
Set up some (artificial) parameters
In a loop, call move1D(), get and print new position, use for next call
Examine manually
CS-2301, D-Term 2014
Introduction

10. Questions?
CS-2301, D-Term 2014
Introduction