Lists

Question 1

Creating lists

Answer 1

List = [1,2,3]

Blist = list (4,5,6)

Question 2

Converting to lists

Answer 2

List(‘cat’)
»> [‘c’, ‘a’, ‘t’]

Or
List(a_tuple). ->. Creates list of values in a_tuple

Question 3

Splitting function

Answer 3

Birthday = ‘1/6/1952’

Birthday.split(‘/’)
»> [‘1’, ‘6’, ‘1952’]

Question 4

Get a list item by using [offset]

Change value by offset

Answer 4

Starts at zero

List[2] = ‘b’
»> changes the 3rd value of list to ‘b’

Question 5

Get a slice to extract items by offset range

Answer 5

List[::2]. ->. Starts at list beginning and goes by 2

List[1:8:3]. ->. Goes from item 2 to item 9, by 3’s

Question 6

Appending lists

Answer 6

List.append(‘value’)

-> appends ‘value’ to end of list

Question 7

Extend function

Answer 7

Merges one list with another

A = [1,2,3]
B = [6,7,8]

A.extend(B)
»> [1,2,3,6,7,8]

Question 8

”+=”

Answer 8

Functions like extend

Merges the items in the lists
(As opposed to append, which would have added the second list as a single list item

A=[1,2]. B=[3,4]
A += B. ->. [1,2,3,4]
A.append(B). ->. [1,2,[3,4]]

Question 9

Insert() function

Answer 9

Adds an item before any offset in a list.

List.insert(3, ‘itema’)
Adds ‘itema’ before item #4

Question 10

Del [ ] function

Answer 10

Deletes an item by offset

Del list[2]. -> deletes the third item in list

Question 11

Remove ( ) function

Answer 11

Removes that item wherever in the list

List.remove(‘cat’). ->. Removes ‘cat’

Question 12

“LIFO”

Answer 12

Last in first out

Data structure or stack.

Append() followed by pop()

Question 13

“FIFO”

Answer 13

First in, first out

Data structure or stack

Pop(0)

Question 14

Index(. ) function

Answer 14

List.index(‘value ‘) -> tells what offset an item is

Question 15

‘Value ‘ in list

Answer 15

Returns True if the value is in list, else False

Question 16

Count(. ) function

Answer 16

Counts how many times a particular value occurs in a list.

List.count(‘value’)

Question 17

Sort() function

Answer 17

Sorts the list in place, changes the list

List.sort()

List.sort(reverse =True). - > reverse sorts

Question 18

Sorted() function

Answer 18

Returns a sorted copy of the list

List_sorted = sorted(list)

Question 19

Len() function

Answer 19

Returns the number of items in a list

Question 20

Ways to copy lists

Answer 20

A = [1,2,3]
B = A.copy()
C = list(A)
D = A[:]

B, C, D are copies of A, changing A does not change the rest and vica versa

Question 21

Tuple

Answer 21

Immutable

Follow all items with a comma, except last item

Question 22

Tuple unpacking

Answer 22

Assigning multiple variables at once

A_tuple = (1,2,3)
a,b,c = A_tuple
-> a is 1, b is 2, etc

Question 23

Tuple() conversion function

Answer 23

Makes tuples of other things

Tuple(list)

Question 24

Dictionary

Answer 24

Created by placing curly brackets around comma separated key:value pairs

Dict = {key:value1, …}

Question 25

dict() function

Answer 25

Converts two-value sequences into a dictionary. The first item in the list is the key, the second item is the value.

Dictionary keys must be unique.

Question 26

Adding to a dictionary

Answer 26

Dict[‘added_value’] = ‘value’

Question 27

Update() dictionary function

Answer 27

Copies the keys and values of one dictionary into another.

Pythons.update(funny_others)

Adds dictionary funny_others to pythons

Question 28

Deleting an item by key with “del[]”

Answer 28

Del dict[‘key’]

Question 29

clear() function for dictionaries

Answer 29

Dict.clear()

Deletes all keys and values from a dictionary

Question 30

Test for a key by using in

Answer 30

Returns True or False

‘Chapman’ in pythons
True

Question 31

Get an item by [key]

Answer 31

Most common use of a dictionary.

Test for key in dictionary first, if present, use:

Dict[‘key’] -> returns value

Question 32

Dictionary get() function

Answer 32

Dict.get(‘key’) -> returns value

Can also provide an optional value, if key exists you get its value; if not, you get the optional value.

Pythons.get(‘Marx’, ‘not a python’)
Will return ‘not a python’

Question 33

Get all keys by using keys() function

Answer 33

Dict.keys()

Returns all keys

Question 34

Get all values by using values ()

Answer 34

Dict.values()

Returns values of all keys in dict

Question 35

Get all key:value pairs by using items ()

Answer 35

Dict.items()

Returns all key:value pairs

Question 36

Lists

Answer 36

Lists are mutable.

Made from zero or more elements, separated by commas, and surrounded by square brackets.

[1,2,3]

Question 37

Set()

Answer 37

Set is like a dictionary with its values thrown away, leaving only the keys.

Use set() function
Or
Enclose one or more comma separated values in curly brackets.

Question 38

zip() function

Answer 38

Iterates multiple sequences in parallel

Ex = creating an English French dictionary
English = []
French []
EF_Dict = dict(zip(English, French))

Question 39

range()

Answer 39

Generates number sequences

For x in range (0,3):
Print(x)

-> creates a sequence from 0 to 2

List(range(0,3)) -> crestes a list of numbers from 0 to 2

Question 40

Comprehensions

Answer 40

A comprehension is a compact way of creating a Python data structure from one or more iterators.

Can combine loops and conditional tests with a less verbose syntax.

Question 41

List comprehension

Answer 41

[expression for item in iterable]

number_list = [number for number in range(1,6)
creates a list from 1-5

[expression for item in iterable if condition]

a_list = [number for number in range(1,6) if number % 2 == 1]
creates a list of odd numbers between 1 and 5

Question 42

List comprehension for rows, cols, cells

Answer 42

rows = range(1,4)
cols = range(1,3)
cells = [(row, col) for row in rows for col in cols]
for cell in cells:
    print(cell)

or
for row, col in cells:
print(row, col)

Question 43

Dictionary comprehensions

Answer 43

{key_expression:value_expression for expression in iterable}

word =’letters’
letter_counts = {letter:word.count(letter) for letter in word}
creates a dictionary of each letter in “letters” and how many times each letter occurs.

Question 44

Set comprehension

Answer 44

{expression for expression in iterable}

a_set = {number for number in range(1,6) if number % 3==1}
returns a list of every third number

Question 45

Generator comprehensions

Answer 45

Tuples do not have comprehensions!

Creates a “generator comprehension”, returns a generator object.
number_thing = (number for number in range(1,6))
type(number_thing)

A generator can only be run once.

A generator is one way to provide data to an iterator.