Python List and Loop

Question 1

Lists

Answer 1

can contain multiple or individual items

You can put items of any type in a list

Separate with commas and surround with [ ]

Lists are kept in order

Question 2

Lists example:

Answer 2

meals = [“artichokes”, “bbq”, “chili”, “donuts”]

*Lists can contain duplicates

[“artichokes”, “bbq”, “chili”, “donuts”, “bbq”]

Good to use plural nouns for variable name (meals not meal)

Question 3

Accessing Items list by Index:

meals = [“artichokes”, “bbq”, “chili”, “donuts”]

Answer 3

meals = [‘artichokes’, ‘bbq’, ‘eggs’]
print(meals[1])
bbq

list = [‘artichokes’, ‘bbq’, ‘eggs]
print (list.index(‘bbq’))
1

Question 4

Adding to Lists

Answer 4

list. append( ) ## append elem at end
list. append(‘shemp’) ## append elem at end
list. insert(0, ‘xxx’) ## insert elem at index 0
list. extend([‘yyy’, ‘zzz’]) ## add list of elems at end

Question 5

How to code adding

Answer 5

list = [ ] ## Start as the empty list

list. append(‘a’) ## Use append() to add elements
list. append(‘b’)

print(list)
>[‘a’, ‘b’,]

or:
print(list.append(‘a’))

Question 6

More Adding methods:

Answer 6

list = [‘larry’, ‘curly’, ‘moe’]

list. append(‘shemp’) ## append elem at end
list. insert(0, ‘xxx’) ## insert elem at index 0
list. extend([‘yyy’, ‘zzz’]) ## add list of elems at end

print (list)
[‘xxx’, ‘larry’, ‘curly’, ‘moe’, ‘shemp’, ‘yyy’, ‘zzz’]

Question 7

Removing from Lists

Answer 7

Remove item from end: pop with nothing in parentheses

list. remove(‘curly’) ## search and remove that element
list. pop(1) ## removes and returns ‘larry’

Question 8

How to code to remove:

Answer 8

list = ['larry', 'curly', 'moe']
print(list.remove("curly"))    or list.remove("curly") 
print(list)
>None
>list = ['larry', 'moe']

or
remove = list.remove(“curly”)
print(list)

Question 9

more code to remove:

Answer 9

list = ['larry', 'curly', 'moe']
print(list.pop(1))    or list.pop(1)
print(list)
>curly
>list = ['larry', 'moe']

or
pop = list.pop( )
print(list)

Question 10

Sorting Lists

Answer 10

list.sort( )
print(sorted(list))

The easiest way to sort is with the sorted(list) function, which takes a list and returns a new list with those elements in sorted order. The original list is not changed.

Question 11

How to code: Sorting

Answer 11

list = [5, 1, 4, 3]
print(sorted(list))
>[1, 3, 4, 5]

or 
list = [5, 1, 4, 3]
list.sort
print(list)
>[1, 3, 4, 5]

Question 12

Reverse sorting code:

Answer 12

list = [2, 1, 3, 5, 6, 4]
list.sort(reverse = True)
print(list) # >[6, 5, 4, 3, 2, 1]

or 
print(sorted(list, reverse = True)) # >[6, 5, 4, 3, 2, 1]

Question 13

Getting List: Length

Answer 13

len(list)

Note: syntax is different than for append, pop, and sort

With len, list_name goes in parentheses

Question 14

How to code: Length

Answer 14

meals = [‘hummus’, ‘ice cream’, ‘grits’]
print(len(meals))
>3

Question 15

Loops

Answer 15

They’re great for repeating code

You decide the condition that ends the loop

Question 16

FOR and IN

Answer 16

The for construct – for var in list – is an easy way to look at each element in a list (or other collection). Do not add or remove from the list during iteration.

The in construct on its own is an easy way to test if an element appears in a list (or other collection) – value in collection – tests if the value is in the collection, returning True/False.