Tuples & Dictionaries (UCSD - Wk 2)

Question 1

how do you pronounce tuple

Answer 1

too pel

Question 2

What is the difference between a tuple and a list?

Answer 2

A tuple is immutable (you can’t change any of the values)

Question 3

What’s the difference in how you instantiate a tuple and a list?

Answer 3

list = [x, y]; tuple = (x, y); can also instantiate a tuple with a list with func: tupleVar = tuple(list)

Question 4

Why is it important that it’s immutable for parallel computing?

Answer 4

Don’t need to account for multiple threads / people using diff data

Question 5

Why is the immumtability important for using tuples with dictionaries?

Answer 5

Tuples can be used as keys in dict. since values don’t change, can org on initial value

Question 6

What is the python equivalent of a map?

Answer 6

Dictionary

Question 7

How can we think about the structure of a dictionary?

Answer 7

It’s like an index: Key Value Pairs, where Key is immutable (value or tuple)

Question 8

What kinds of objects can you store in the value of a dictionary?

Answer 8

Any. ints, lists, even other dictionaries

Question 9

how do you initialize a dictionary?

Answer 9

dict = {key1:value1, key2, value2}

Question 10

how do you initialize a dict with a tuple as a key

Answer 10

dict = {(key1A, key1B): value1, … }

Question 11

lookup value for key1 in dict

Answer 11

dict[ key1 ]

Question 12

How do you add to a dictionary

Answer 12

create a new key / value pair. If key already in use, over-writes value

Question 13

is there a fixed order for dictionaries?

Answer 13

no. (one of the reasons they’re fast to lookup)

Question 14

What happens if you try to retrieve a value for a dict where the key does not exist?

Answer 14

get a run-time error

Question 15

What’s a safer way to retrieve an element from a dictionary if you’re not sure if the key exists

Answer 15

x = dict.get(key); Returns None if key non-existent

Question 16

Test to see if a key is in a dictionary

Answer 16

key1 in dict; returns bool

Question 17

how to retrieve and delete value with key1 in dict

Answer 17

dict.pop(key1)

Question 18

how to just delete value with key from dict

Answer 18

del dict[key1]

Question 19

iterate over keys in a dictionary

Answer 19

for i in dict: print(i)

Question 20

iterate over key values in a dictionary

Answer 20

for key, value in dict.items(): print(key, “:”, value)

Question 21

can you change a dict while iterating through it?

Answer 21

no.

Question 22

how do you remove a set of items from a dict with iteration?

Answer 22

iterate through appending keys to remove to a new list, then iterate through the list, popping items from orig dict

Question 23

how to build a list with squares from 1 to 10 (eg of “comprehension”)

Answer 23

list = [i**2 for i in range (1,11)] > can use an iteration and values here

Question 24

How to create a list with random numbers (after import random package)

Answer 24

list = [random.randint(0,5) for i in range (x,y)]

Question 25

how do you build a dictionary using comprehension

Answer 25

dict = {key : value for i in range (0,10)}

Question 26

What are some distinguishing features of sets

Answer 26

unique elements, un-ordered (allowing to be very fast), and useful math operations

Question 27

how do you initialize a set

Answer 27

setVar = set([‘blue’, ‘green’, ‘red’]) or set(list)

Question 28

how do you add an element to a set

Answer 28

setVar.add(value)&raquo_space; if you add an element that already exists, no change (no error)

Question 29

how do you discard an element from a set

Answer 29

setVar.discard(value)&raquo_space; if not there, does nothing and no error

Question 30

return all elements that in two sets

Answer 30

eitherSetVar = set1.union(set2)&raquo_space; just returns all unique values

Question 31

return elements that are common to both sets

Answer 31

bothSetVar = set1.intersect(set2)

Question 32

Alternatives to union and intersect methods

Answer 32

OR ( | ) and AND ( & ) operators&raquo_space; set1 | set2; set1 & set2