Programming Tutorials

Variables And Names in Python

By: Zed A. Shaw  

Now you can print things with print and you can do math. The next step is to learn about variables. In programming a variable is nothing more than a name for something so you can use the name rather than the something as you code. Programmers use these variable names to make their code read more like English, and because they have lousy memories. If they didn’t use good names for things in their software, they’d get lost when they tried to read their code again.

1. Write a comment above each line explaining to yourself what it does in English.
2. Read your .py file backwards.
3. Read your .py file out loud saying even the characters.
1 cars = 100
2 space_in_a_car = 4.0
3 drivers = 30
4 passengers = 90
5 cars_not_driven = cars - drivers
6 cars_driven = drivers
7 carpool_capacity = cars_driven * space_in_a_car
8 average_passengers_per_car = passengers / cars_driven
9
10
11 print "There are", cars, "cars available."
12 print "There are only", drivers, "drivers available."
13 print "There will be", cars_not_driven, "empty cars today."
14 print "We can transport", carpool_capacity, "people today."
15 print "We have", passengers, "to carpool today."
16 print "We need to put about", average_passengers_per_car, "in each car."

Note: The _ in space_in_a_car is called an underscore character. Find out how to type it if you do not already know. We use this character a lot to put an imaginary space between words in variable names.

What You Should See

$ python ex4.py
There are 100 cars available.
There are only 30 drivers available.
There will be 70 empty cars today.
We can transport 120.0 people today.
We have 90 to carpool today.
We need to put about 3 in each car.
$