Chapter 11 Dictionaries

Question 1

A dictionary contains a collection of indices which are called?

Answer 1

Keys

Question 2

The association of a key and a value is called a? Or sometimes a?

Answer 2

Key-value-pair or sometimes item

Question 3

In a dictionary, each key “ “ a value

Answer 3

maps to

Question 4

Dictionaries are always in alphabetical order. True or False

Answer 4

False
Dictionary elements are in no particular order, unlike lists.

Question 5

” “ is a method that takes a key and default value. If the key appears in the dictionary, the method returns the corresponding value; otherwise, it returns the default value.

Answer 5

.get

Question 6

To traverse the keys in alphabetical order, you can use
the built-in function

Answer 6

sorted

Question 7

Define singleton

Answer 7

A list that contains a single element.

Question 8

How do I tell Python that I want the variable outside of the function to be used inside the function without alterations?

Answer 8

Use the global statement
»> been_called = False
»> def example2():
global been_called
been_called = True

Question 9

What is wrong with this code?
»> count = 0
»>def counter():
count = count + 1
print(count)

Answer 9

The global variable was not declared inside the function.
Corrected version:
»> def counter():
global count
count += 1
print(count)

Question 10

True or False:
If a global variable refers to an immutable value, you can modify the value without declaring the variable.

Answer 10

False. The value must be mutable.
Example:
known = {0:0, 1:1}

def example():
known[2] = 1

Question 11

4 suggestions for debugging large datasets are:

Answer 11

1. Scale down the input
2. Check summaries and types
3. Write self-checks
4. Format the output
   Page 111-112 of Think Python

Question 12

A relationship in which each element of one set corresponds to an element of
another set.

Answer 12

mapping

Question 13

A mapping from keys to their corresponding values

Answer 13

dictionary

Question 14

An object that appears in a dictionary as the first part of a key-value pair.

Answer 14

key

Question 15

In a dictionary, another name for a key-value pair

Answer 15

item

Question 16

The representation of the mapping from a key to a value

Answer 16

key-value pair

Question 17

An object that appears in a dictionary as the second part of a key-value pair. This is more specific than our previous use of the word.

Answer 17

value

Question 18

The algorithm used to implement Python dictionaries.

Answer 18

hashtable

Question 19

A function used by a hashtable to compute the location for a key.

Answer 19

hash function

Question 20

A way of performing a computation.

Answer 20

implementation

Question 21

A type that has a hash function. Immutable types like integers, floats and strings are “______”; mutable types like lists and dictionaries are not.

Answer 21

hashable

Question 22

A dictionary operation that takes a key and finds the corresponding value.

Answer 22

lookup

Question 23

A dictionary operation that takes a value and finds one or more keys that map to it.

Answer 23

reverse lookup

Question 24

A statement that (deliberately) raises an exception

Answer 24

raise statement

Question 25

A list (or other sequence) with a single element.

Answer 25

singleton

Question 26

A diagram that shows every frame created during the execution of a program,
with an arrow from each caller to each callee.

Answer 26

Call graph

Question 27

A computed value stored to avoid unnecessary future computation.

Answer 27

memo

Question 28

A variable defined outside a function. Can be accessed from any function.

Answer 28

global variable

Question 29

A boolean variable used to indicate whether a condition is true.

Answer 29

flag

Question 30

A statement like global that tells the interpreter something about a variable.

Answer 30

declaration