Python 1: Variables and I/O

Learning Goals:

 

By the end of this lesson you should be able to:

1.     Describe what a variable is.

2.     Identify the basic Data Types.

3.     Write to the screen

4.     Process User input.

 

 

Variables

 

Variables are a location in memory that can hold information.   Variables always have a name and a type.   Basic variable types that you will be using are:

 

int -  Numbers without decimals. Like 6 or 7

 

float- Numbers that can have decimals. Like  3.14

 

string – A group of Characters.   Like “dog”, “cat” or “4353 George K”

 

2 Weird things about Python:

 

1.     In Python, you don’t need to “declare” variables you can just use them.

 

Examples: 

n=1

print n

 

pet= “dog”

print dog

myScore= 56.9

 

Note 1: the ‘=’ sign is used to assign a value to a variable.   

 

Note 2: Variable names should:

·        Be meaningful

·        always start with a lower case letter

·        subsequent words should be capitalized

 

2.     Variables can change type in the middle of a program.

I don’t know of any other languages that do this… but Python lets you, for example, use a variable to hold an int for a while then you can start using it as string if you feel like it.

Getting User Input

 

The function raw_input() will get a value from the user.  Use it like this:

 

print ('Enter Your Name:')

 

userName=raw_input()

 

print ('Your name is' + userName)

 

This program gets the name from the user, stores it in userName and displays it on the screen.

 

Note: raw-input()  will bring in the user’s value as a string.  If you want to use it as a number you will need to convert it to an int or float like this.

 

print (‘Enter a Number’)

 

num=int(raw_input())

 

print (num*5)

 

 

 

 

Programs

Save each program in you unit 1 folder as a text document called A1Px where x is the program number.  Then copy and paste it into the python interpreter.   Use the # symbol in include your name and the program code at the top of your script.

 

Ex:  #Tony Demello A1P1

 

Program 1 – Echo

Write a program that prompts the user to enter some words then echo it back on the screen.

 

Program 2 – The Multiplier

Prompt the user to enter 2 numbers, multiply them and report the result with an appropriate comment.

 

Program 3- Average Score

Prompt the user to enter 5 scores.  Calculate the average and display the result.

 

Program 4- Madlib

Prompt the user to enter 3 nouns, 3 adjectives and 3 past tense verbs (ran, fell etc).   Write a short story (3 sentences tops) that uses the user’s words.   Something like this:

 

The adjective1 noun2 verb3 neatly on a adjective3 noun1. Suddenly it verb2 into a big pile of adjective 2 noun3.   The adjective1 noun2 verb 1 all the way to its mom.

 

 

Show Mr.Kurz all 4 programs when you are finished.