Lecture 3

Question 1

define dictionary

Answer 1

A data structure that consists of key-value pairs.

We use the keys to describe our data and the values to represent the data.

Keys are usually numbers or strings; values can be any data type

Question 2

strip method syntax+ function

Answer 2

stringname.strip(characters to remove)

removing characters from the beginning or end of a string for characters supplied as arguments

OR

if no argument passed, will remove only leading and trailing spaces in a string

Question 3

how can you add a key-value pair to a dictionary?

Answer 3

1. define dictionary d={}
2. d[“key1”] = “value1”

Question 4

how can you initialize a dictionary using typecasting?

Answer 4

d = dict()

Question 5

how do you combine 2 lists into a dictionary using iteration and one variable?

Answer 5

1. define both lists
2. define range + variable
3. key-value assignment formatting: d[l1[i]] = l2[i] NOTE brackets around key, none around value. if you add brackets around the value it will print with brackets!*

Question 6

how do you use a range loop to print ONLY the values in a dictionary?

Answer 6

dictionaryname={}
for i in dictionaryname.values():
print(i)

Question 7

how do you use a loop to print ONLY the keys in a dictionary?

Answer 7

dictionaryname={}
for i in dictionaryname.keys():
print(i)

Question 8

how do you use a loop to print the KEY-VALUE PAIRS in a dictionary?

Answer 8

dictionaryname={}
for i in dictionaryname.items():
print(i)

Question 9

how do you print a LIST of TUPLES containing the key-value pairs in a dictionary?

Answer 9

print(list(dictionaryname.items()))

NOTE: you must typecast to a list or it will auto preface with “dict_items”. will still print a list of tuples

Question 10

mutability and ordered/unordered? [ ]

Answer 10

[] - mutable and ordered

Question 11

mutability and ordered/unordered? { }

Answer 11

{} - unordered, mutable, key-value pairs

Question 12

mutability and ordered/unordered? “ “

Answer 12

”” - ordered, immutable

Question 13

mutability and ordered/unordered? ( )

Answer 13

() - ordered, immutable

Question 14

how do you access the values in a dictionary?

Answer 14

using the corresponding keys

Question 15

update method function and syntax

Answer 15

appends dictionary 2 to the end of dictionary 1. can also pass another iterable object (usually of tuples containing key-value pairs)

dict1.update(dict2)

Question 16

fromkeys method function and syntax

Answer 16

fromkeys creates a dictionary from the given sequence of keys and one value argument

dict.fromkeys(key list, value)

Question 17

how do you use a range loop to create a dictionary using indexing?

Answer 17

names = [“john”, “ala”, “ilia”, “sudan”, “mercy”] #define list of keys
marks = [100, 200, 150, 80, 300] #define list of values
dictionary: d = {} #define dictionary
for i in range([# of key-value pairs-1]):
d[names[i]] = marks[i]

Question 18

how do you use a range loop to create a list of lists where the pairs are assigned in order?

Answer 18

l1=[x num of elements]
l2=[x num of elements]

l3=[]

for i in range len(l1):
l3.append(l1[i], l2[i])

Question 19

how do you use a range loop to create a dictionary using 2 defined variables in the range statement?

Answer 19

dict1={}

for (i,j) in l:
dict1[i] = j

Question 20

how do you remove a key-value pair from a dictionary?

Answer 20

dictionaryname.pop(keyname)

Question 21

how do you rename a key in a dictionary?

Answer 21

d[‘newkey’] = d.pop(“oldkey”)

Question 22

how do you use a dictionary to count the number of occurrences of an element?

Answer 22

l=”Hello world”
x=0
d=dict.fromkeys(l, x) #create a dictionary using fromkeys and initialize every occurrence to 0. no duplicate keys by default

for i in l: #loop across sequence
d[i] = d[i]+1 #add 1 to the key-value pair for every occurrence of the sequence

Question 23

define set. ordered or unordered? mutable/immutable?

Answer 23

a collection of unique data, meaning that elements within a set cannot be duplicated.

UNORDERED and MUTABLE

Question 24

add method syntax + function

Answer 24

used to add an element to a set.

setname.add(element)

Question 25

remove/discard methods syntax + function

Answer 25

remove() will raise an error if the specified item does not exist, and discard() will not.

Question 26

copy method syntax + function

Answer 26

returns a copy of the original set. As the copied list is shallow, any changes made to the new list will not be reflected in the original list.

setname.copy()

Question 27

clear method syntax + function

Answer 27

Removes all elements from the set

setname.clear()

Question 28

intersection method syntax + function

Answer 28

Finding the values present in both the sets

set1.intersection(set2)

Question 29

difference update method + function

Answer 29

Given two Python sets, update the first set with items that exist only in the first set and not in the second set.

s1.differenceupdate(s2)

you can also pass a full set through s2:

s2.difference_update({7,17})

Question 30

symmetric difference update syntax and function

Answer 30

symmetric_difference_update returns a new set containing only the elements that are NOT common to both sets. like the non-overlapping parts of a venn diagram.

A.symmetric_difference_update(B)