Types and objects

Question 1

What three things does every python object have?

Answer 1

Value, type, ID

Question 2

Explain mutability vs immutability

Answer 2

The value of a mutable object can be changed, whereas an immutable object has the same value for its whole life.

Question 3

Give three examples of mutable objects

Answer 3

Dictionary, set, list

Question 4

Give four examples of immutable objects

Answer 4

String, integer, tuple, float

Question 5

If we assign a=b, explain what happens if b is immutable vs mutable.

Answer 5

a = b creates a copy of b. a = something else sets a to a different object if b is immutable. Changing a mutable object means it can have the same ID, so a would change too.

Question 6

How would you find the number of references to an object?

Answer 6

import sys

sys.getrefcount(object)

Question 7

How does the garbage collector in Python work?

Answer 7

Once objects have no references, they are deleted from memory.

Question 8

Explain the difference between the ‘is’ operator and the ‘==’ operator

Answer 8

is : compares IDs of left and right object.

== : compares values of left and right object

Question 9

What does it mean to say that in Python, all objects are first class?

Answer 9

All variables that can be named can be treated like data.

Question 10

Name 5 categories for representing data in python, give examples of each

Answer 10

None: None
Numbers: int, float
Sequence: list, tuple, string, generator
Mapping: dict
Set: set

Question 11

Name 5 operations on sequence types?

Answer 11

len()
slicing [:] (\_\_getitem\_\_)
in
concatenation +
copying *
aggregation (min, max,...)

Question 12

What is the criterion for a key to be valid in python?

Answer 12

It must be hashable/immutable

Question 13

How would you get the keys, and the values of a dictionary?

Answer 13

dict.keys()
dict.values()
for key, value in dict.items()

Question 14

Name 5 operations that can be performed on set types?

Answer 14

intersection
union
difference
issubset
isdisjoint

Question 15

Name 3 categories of types for representing program structure.

Answer 15

Classes, callables (functions, methods), modules

Question 16

How can you tell if an object is callable?

Answer 16

callable(object)

Question 17

Name 5 string methods

Answer 17

string. count()
string. replace()
string. strip()
string. find()
string. upper()
string. lower()