COMP 110 QUIZ 03

Ordered data structure allowing duplicates

list

Check if a key exists in a dictionary

if "key" in my_dict:

Which is faster for checking if an item exists: list or set

set

Code to count word frequencies using a dict

counts = {}
for word in words: 
	counts[word] = counts.get(word, 0) + 1

Add an element to a set

my_set.add("item")

Loop through a dict's keys and values

for key, value in my_dict.items(): 
	print(key, value)

Output of len(set([1,2,3,2]))

3 (sets remove duplicates)

Best data structure for a shopping cart

list (ordered, allows duplicates)

Best data structure for username→userID mapping

dict (key-value pairs)

Best data structure for unique visitor IPs

set (uniqueness)

How to remove 'apple' from this set? fruits = {'apple', 'banana'}

fruits.remove("apple")

Error with print(my_dict["c"]) if "c" doesn't exist

KeyError (use my_dict.get("c"))

Create an empty set

my_set = set() NOT {}

Add a key-value pair to a dict

my_dict["new_key"] = value

Check if a value exists in a list

if value in my_list:

Remove duplicates from a list

list(set(my_list)) (order not preserved)

Output of {"a":1, "b":2} == {"b":2, "a":1}

True (dicts compare key-value pairs, not order)

How to get all keys from a dictionary

my_dict.keys()

Merge two sets

set1.union(set2)

Delete a key from a dict

mydict.pop("key")