A Quick and Easy Python Tutorial
This is a translation from a 90 minute class I held on the basics of Python scripting. A download link for the PowerPoint .pptx file is at the bottom of the article.
About Python
- Developed by Guido van Rossum
- First released in 1991
- High Level
- OOP*
- Platform Independent
- Great community
- Free and Open Source
- Easy to learn
Python Applications
- Console / Scripts
- GUI
- Web
Environment
- Lubuntu VM
- Python 2.7 with IDLE
- IDLE is a basic Integrated Development Environment (IDE) for Python
Interactive vs. Script Mode
We will start with interactive mode which gives us immediate feedback
# python3
>>>
Most programmers program Python in script mode. In script mode you can write, edit, load, and save your programs
# python3 script.py
Our First Program – “Why do witches burn?”
Open Python in interactive mode and type:
>>> print(“Why do witches burn?”)
What happens?
Print is a function, everything within parenthesis are arguments
Functions are subroutines that can be reused for common tasks, such as printing to the console
Our First Program - Again
Let’s write our first program in script mode
print(“Why do witches burn?”)
input(“Press enter for the answer”)
print(“Because they’re made of wood.”)
Save the file as riddle.py, and from another console, type:
# python3 riddle.py
Exercise 1
≈5 Minutes
Edit riddle.py to display the following every time it is run:
Riddle Program
By: [Your Name], accompanied by a(n) [adjective] [your spirit animal]
[new line]
Solution
print(“Riddle Program”)
print(“By: Bradford, accompanied by a corpulent camel spider”)
print()
Comments
Comments are ignored by Python, but are invaluable for programmers.
Indicated by #:
# I’m a comment.
# print(“I’m also a comment”)
Exercise 2
≈3 Minutes
Edit riddle.py to notate the following:
The name of your program
The name of the developer
The date the script was created
Solution
# Riddle Program
# Bradford
# 15 July 2015
Documentation
Input
Now let’s get input from the console.
input([prompt])
If the prompt argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that.
https://docs.python.org/3.2/library/functions.html?highlight=input#input
name = input(“WHAT... is your name?”)
print(“Your name is”, name)
Blocks
Blocks are one or more consecutive lines that form a single unit.
Other languages (C, C++, C#, Java) require curly braces {} to indicate the beginning and the end of a block.
Python uses indentation to create blocks —
Indentation can be either:
- A combination of spaces (most common & recommended is 4 spaces)
- A single tab
Most important rule: DON’T MIX INDENTATION STYLES
Decision Making - Conditional Statements
If statement:
if [condition]:
[do action]
elif [condition]:
[do action]
else:
[do action]
How does Python know when a conditional action ends?
If statement:
swallow = “european"
if swallow == “african":
print(“It could grip it by the husk.”)
elif swallow == “european”:
print(“They could carry it on a line.”)
else:
print(“Are you suggesting coconuts migrate?”)
Exercise 3
≈10 Minutes
Edit riddle.py to perform the following:
- Prompt for the user to select a riddle by typing a 1 or 2
- Based on the input, display a riddle
- Output an error if input either than “1” or “2” is entered
Solution
number = input("Which riddle would you like to hear? Enter 1 or 2: ")
if number == “1”:
print(“Why do witches burn? Because they’re made of wood!")
elif number == “2”:
print(“What is your favorite color? I don’t know!")
else:
print(“Ni!")
Loops
While Loop
while [condition]:
[loop body]
The loop will execute the loop body until the condition is no longer true.
limbs = 4
print(“None shall pass.”)
while limbs > 0:
print(“C’mon ya pansy!”)
print(limbs, “limbs left”)
limbs -= 1
print(limbs, “limbs left”)
print(“Alright, we’ll call it a draw.”)
What does the above loop do?
Exercise 4
≈10 Minutes
Edit riddle.py to perform the following:
Ask the user a riddle. Implement a loop that continues to loop until the user provides the right answer.
Bonus: make the input case-insensitive [string.lower()]
Functions
Let’s create our own function, print_riddle, in our riddle.py:
def print_riddle():
print(“Why do witches burn?”)
print(“Press enter for the answer”)
print(“Because they’re made of wood.”)
print_riddle()
How does Python know when the function begins? Ends?