1. CS1022 Computer Programming & Principles
Lecture 2.2
A brief introduction to Python (2)

2. Plan of lecture Intro to Portable Python
Integrated development environment (IDE)
Edit-run workflow
From maths to pseudo-code to Python
Codecademy
Learning to learn
What next?
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3. Portable Python A pre-configured Python distribution
Runs directly on Windows from a USB device
Portable, lightweight, hassle-free
No need to fiddle with class paths, access rights
Large set of libraries bundled together
No need to get these separately
Drawbacks:
Only for Windows
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4. Portable Python (2) We’ll cover the basics of the IDE
Editor and edit-run loop
Making sense of mistakes
Here’s what you should have:
Double-click on
“PyScripter-Portable.exe”
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5. Python interpreter pane
Portable Python (3)
Here’s what you should see:
Files pane
Editor pane
Python interpreter pane
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6. Portable Python (4) 2 1 3 Basic edit-run loop: What kinds of problems?
Load a file
Edit it (editor gives feedback)
Run it
If there are problems, go to 2
else stop
What kinds of problems?
Program aborts (does not run)
Program runs but does not do what we intended 1 2 3
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7. Editing a Python program
Let’s edit a new Python program:
Highlight the text in 2
Delete all of it
Type the following in 2 1 2 3
# absolute value
n = -20
if n < 0:
abs = -n
else:
abs = n
print(abs)
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8. Running a Python program
To run the program we typed, we can:
Type <ctrl-F9> or click on green arrow above pane 2
Program will be run in pane 3
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9. Running a Python program (2)
If we wanted to try the previous program with different values we would have to edit line 1
Instead, we can provide parameters from keyboard
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10. Editing a Python program (revisited)
Let’s edit our Python program and add the following:
import “argv” (functionality) from module “sys”
from sys import argv
# absolute value
n = int(argv[1])
if n < 0:
abs = -n
else:
abs = n
print(abs)
from sys import arg
# absolute value
n = -20
if n < 0:
abs = -n
else:
abs = n
print(abs)
Get first parameter and convert it into an integer
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11. Parameters from keyboard
“argv” allows us to read data from keyboard
Data are parameters which we assign to variables
It is possible to write programs without parameters
We need to initialise variables in the program
“initialise” = “give initial values”
Every time we want to try different values we need to change these
This is tedious...
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12. Parameters from keyboard (2)
We need to tell Python we want to use parameters:
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13. Parameters from keyboard (2)
And provide the actual value(s)
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14. Defining functions
By defining a function we can pass parameters from the interpreter line:
def absolute(n):
if n < 0:
abs = -n
else:
abs = n
return(abs)
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15. Defining functions
In the IDE:
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16. Formatting your program
The editor helps you formatting your program
Indentations are important!
You still need to confirm what the editor does
For instance, when the “if” command is finished
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17. Program with a “for” loop
# sum first n integers
n = int(argv[1])
sum = 0
for i in range(1,n):
sum = sum + i
print(sum)
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18. Program with a “while” loop
Let’s write a program to count down from an input n to 0
We must use a while-loop!
while condition:
statement
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19. Further reading Python’s official Web site https://www.python.org/
Wikipedia’s entry on Python
Codecademy on-line Python training
Python Humour! (who said we are not fun/funny?)
Portable Python
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