Python

Question 1

What is MRO?

Answer 1

Method Resolution Order - the order in which base classes are searched when looking for a method or an attribute. In Python the MRO for most cases is depth first then left to right and remove all duplicates except the last one.

Question 2

What is the output?
class First(object):
def __init__(self):
super(First, self).__init__()
print(“first”)

class Second(object):
def __init__(self):
super(Second, self).__init__()
print(“second”)

class Third(First, Second):
def __init__(self):
super(Third, self).__init__()
print(“third”)

Answer 2

second
first
third

Question 3

What are the steps in creating an instance of a class?

Answer 3

Python calls its __new__ method to create the object then calls __init__ on the object that is returned. The __new__ looks like this:
def __new__(cls):
return super().__new__(cls)
If new returns an inst of a diff class, then __init__ is not called

Question 4

What should init return?

Answer 4

None, anything else will throw an error

Question 5

Add unit property to immutable built-in float.

Answer 5

class MyFloat(float):
def __new__(cls, value, unit):
instance = super().__new__(cls, value)
## customize here
instance.unit = unit
## return instance
return instance
## in immutable types value is set in __new__, so overwriting __init__ with unit would cause error

Question 6

What are 2 ways to create a singleton?

Answer 6

1. Module level constant
2. overwrite __new__ (__init__ won’t get called)

Question 7

What is variable casting?

Answer 7

A cast is a way of explicitly informing the compiler that you intend to make the conversion and that you are aware that data loss might occur, or the cast may fail at run time.

Question 8

Python is … typed language

Answer 8

dynamically

Question 9

n = 300
id(n) == ?

Answer 9

returns location of the int object 300 in memory

Question 10

What is small integer caching?

Answer 10

small integer in python is -5 to 256
At startup of the interpreter session, python creates objects for all small integers. This is done to improve performance (because these objects are used so much)

Question 11

What is the first class O?

Answer 11

a first-class citizen (also type, object, entity, or value) in a given programming language is an entity which supports all the operations generally available to other entities. These operations typically include being passed as an argument, returned from a function, and assigned to a variable.

Question 12

What is introspection?

Answer 12

The ability to determine the type of an O at runtime.

Question 13

What is callable? Which types are callable in Python.

Answer 13

Callable is a type that can be executed. Functions and classes are callable in Python.

Question 14

What is LEGB rule?

Answer 14

When resolving a name, python looks in 1. local scope, 2. in enclosing function, 3. in global scope, 4. in built-in scope

Question 15

What are decorators can be used for?

Answer 15

1. Prevent duplication of code
   Timing how long a function runs
2. Setting the frequency of a function run
3. Memoization - caching of function results, so they don’t have to be called again (ex. 2+2 will always be 4)
4. Setting an attribute for multiple unrelated classes without using inheritance.
5. Register function as a plugin

Question 16

What is Big O. What is the best complexity.

Answer 16

A notation used to describe the computational complexity of an algorithm, consists of 2 parts: time and space
the best complexity is O(1)
O stands for order of approximation

Question 17

What is the difference between integration and acceptance testing?

Answer 17

acceptance testing is performed in the environment that is as close to production as possible

Question 18

What is the diff between VM and container?

Answer 18

A container is a software code package containing an application’s code, its libraries, and other dependencies. Containerization makes your applications portable so that the same code can run on any device. A virtual machine is a digital copy of a physical machine.

Question 19

Why can’t a python class have methods with duplicate names?

Answer 19

All attributes are stored in __dict__ and dictionaries cannot have duplicate keys - hence no overloading.

Question 20

Is this allowed:
def add_item(x, sum=1, y):
pass

Answer 20

No, default params cannot be followed by regular params

Question 21

Which data types are mutable in Python?

Answer 21

1. Lists
2. Dicts
3. Sets
4. All custom objects
5. byte array (can be used as a mutable str)
   Collections internally keep references to all their individual values. This opens the opportunity for mutability.

Question 22

Can mutable types be used as default parameters?

Answer 22

Technically, yes, but it shouldn’t be done.
When you call a function with a mutable object as an argument, the function may perform mutations on that object. These mutations will affect the original object outside the function.
def add_item(item, quantity, shopping_list={}):
shopping_list[item] = quantity # next time the function is called with default param, the shopping list will not be empty - it will contain the item

Question 23

What are the immutable data types?

Answer 23

Cannot be modified after creation. Use up a lot of memory. Helpful for multi-threading - no risk of conflict.
1. str
2. typle
3. frozen set
4. Single-item data types, such as integers, floats, complex numbers, and Booleans, are always immutable. So, you have no way to change the value of these types. You just have the option of creating a new object with a new value and throwing away the old one.

Question 24

Given a tuple:
t = (1, [‘a’, ‘b’, ‘c’], “two”], “two”)
which on of these produces an error:
1. t[0] = 2
2. t[1][0] = ‘w’
3. t[2][0] = ‘w’

Answer 24

1. TypeError - tuple o doesn’t support item assignment
2. OK - list is mutable (immutability in python is not transitive)
3. TypeError - str O doesn’t support item assignment

Question 25

What are the 3 fundamental characteristics on a python O?

Answer 25

1. Value
2. Identity (location in memory - read only, cannot be changed)
3. Type

Question 26

What is a mutable object?

Answer 26

if you can change the value of that object without changing the object’s identity, then you have a mutable object.

Question 27

What is in-place algorithm?

Answer 27

Transforming the content of a given data structure by operating on the data structure itself and without using or creating any auxiliary similar data structure.

Question 28

Write code for creating a mutable string.

Answer 28

greeting = “Hello!”
mutable_greeting = bytearray(greeting.encode(“utf-8”))
mutable_greeting[1] = ord(“E”)

Question 29

What is the difference between nonlocal and global?

Answer 29

Global is used to access and modify global variables from within a function, while nonlocal is used to access and modify variables from the nearest enclosing scope that is not global.

Question 30

What is a mapping?

Answer 30

A mapping is a data type that has paired values as items, such as a dictionary.

Question 31

What is the difference between * and ** unpacking operators.

Answer 31

• • unpacks any iterables
    ** - unpacks mappings

Question 32

The output?
my_list = [1, 2, 3, 4, 5, 6]

a, *b, c = my_list

print(a)
print(b)
print(c)

Answer 32

1
[2, 3, 4, 5]
6

Question 33

Merge 2 lists using the unpacking operator:
my_first_list = [1, 2, 3]
my_second_list = [4, 5, 6]

Answer 33

my_merged_list = [*my_first_list, *my_second_list]

Question 34

merge 2 dicts using unpacking operator
my_first_dict = {“A”: 1, “B”: 2}
my_second_dict = {“C”: 3, “D”: 4}

Answer 34

my_merged_dict = {**my_first_dict, **my_second_dict}

Question 35

Whats the output of
x = range(3, 10, 2)
for n in x:
print(n)

Answer 35

3
5
7
9

Question 36

what does the idiom if __name__ == “__main__” do?

Answer 36

It Allows You to Execute Code When the File Runs as a Script, but Not When It’s Imported as a Module

Question 37

Explain different method types in Python.

Answer 37

1. instance method -> can modify both class and instance state
   def some_method(self):
   …
2. class method -> can modify class state, but has no access to self
   @classmethod
   def some_method(cls):
   …
3. static method -> no access to self or cls
   @staticmethod
   def _some_method(x):
   …

Question 38

Give example of @classmethod use

Answer 38

can be used to simplify initialization of different instance types
class Pizza:
def __init__(self, ingredients):
self.ingredients = ingredients
@classmethod
def make_margherita(cls):
return cls([tomato, cheese])

Question 39

Give example of @staticmethod use

Answer 39

For round objects, could be used to return circle area:
class Pizza:
@staticmethod
def _circle_area(r):
return r ** 2 * math.pi

Question 40

What is a package?

Answer 40

A collection of modules

Question 41

What is Conda?

Answer 41

A tool for creating virtual env - part of Anaconda virtual env

Question 42

What is a namespace?

Answer 42

collection of currently defined symbolic names along with information about the object that each name references.

Question 43

What is scope?

Answer 43

the region of a program in which variable name has meaning.

Question 44

2 ways to create branch in git

Answer 44

1. git branch <banrch-name></banrch-name>
2. git checkout -b <branch-name></branch-name>