DS4UX (Spring 2016)/Day 3 follow up

Here are some important concepts that we didn't have a chance to go into in great detail last week. You can use the sections below to review the concepts individually. You can also review how they work together in math_game.py.

Generating a list of numbers easily with range()

>>> range(5)
[0, 1, 2, 3, 4]
>>> for i in range(5):
...     print("Hi" * i)
...

Hi
HiHi
HiHiHi
HiHiHiHi

The range() function returns a list of numbers. This is handy for when you want to generate a list of numbers on the fly instead of creating the list yourself.

>>> range(5)
[0, 1, 2, 3, 4]

Use range when you want to loop over a bunch of numbers in a list, or perform an operation a certain number of times:

>>> numbers = range(5)
>>> for number in numbers:
...     print(number * number)
...
0
1
4
9
16

We could rewrite the above example like this:

>>> for number in range(5):
...     print(number * number)
...
0
1
4
9
16

You can also set the start, end, and increment value (called "step") for a range.

>>> for i in range(2,20,2):
...         print(i)
2 
4
6
8
10
12
14
16
18

Get user input with input()

>>> for i in range(100):
...     my_input = input("Please type something> ")
...     if my_input == "Quit":
...         print("Goodbye!")
...         break
...     else:
...         print("You said: " + my_input)
... 
Please type something> Hello
You said: Hello
Please type something> How are you?
You said: How are you?
Please type something> Quit
Goodbye!
>>>

Iterating an indeterminate number of times with while loops

grocery_list = []
testAnswer = input('Press y if you want to enter more groceries: ')
while testAnswer == 'y':
    food = input('Next item:')
    grocery_list.append(food)
    testAnswer = input('Press y if you want to enter more groceries: ')

print('Your grocery list:')
for food in grocery_list:
    print(food)