Python

Question 1

How python manage memory?

Answer 1

Garbage Collection: Automatically managed, no need manual garbage collection
Reference Counting  If number of reference counters to an object is zero, garbage collector will invoke and clean the memory.

A new stack frame is created when invoking a function and deleted as soon as it return something
Garbage collector will clean up the zero reference counted objects and instance variables.

Question 2

What is heap memory?

Answer 2

Objects and instance variables are created on heap memory

Question 3

What is stack memory

Answer 3

methods and variables are created in stack memory

Question 4

What is the difference between a list and a tuple?

Answer 4

List
[1,3,4,20,5] (usually same kind, can be any kind though)
Mutable (Can change after creation)
Have order (usually same data type)

Tuple
(15,5.8,’Sumedhe’) # age, height, name
Un-mutable
Have structure (usually different data types)

Question 5

How is string interpolation performed?

Answer 5

3 ways to do it.

x = ‘abc’

1. print(f’Hello {x}’)
2. print(‘Hello %s %s’ %(x,x))
3. print(“Hi {}”.format((name)))

Question 6

What is the difference between is and ==

Answer 6

is  - Check identity
== check equality
a =[1,2,3]
b = a
c=[1,2,3]

a==b –True
a==c – True

a is b – True
a is c – False (because a and c are not pointed to the same object, doesn’t have the same ID)

Question 7

What is the decorator

Answer 7

A decorator allows adding functionality to an existing function by passing that existing function to a decorator, which executes the existing function as well as additional code.

ex @logging operator automatically start logging

Question 8

What is range function?

Answer 8

A function to generate a list of integers
• list(range(5))  [0,1,2,3,4]
• list(range(2,10))  [2,3,4,5,6,7,8,9]
• list(range(2,10,2))  [2,4,6,8]

Question 9

Define class named car with 2 attributes, color and speed. Create a instance and return speed.

Answer 9

class car():
  def \_\_init\_\_(self, color, speed):
      self.color = color
      self.speed = speed

car = Car(‘red’,’100mph’)
print(car.speed)

Question 10

What is the difference between instance, static and class methods in python?

Answer 10

Instance methods : accept self parameter and relate to a specific instance of the class.
Static methods : use @staticmethod decorator, are not related to a specific instance, and are self-contained (don’t modify class or instance attributes)
Class methods : accept cls parameter and can modify the class itself

Question 11

What is the difference between func and func()

Answer 11

• func is the object representing the function which can be assigned to a variable or passed to another function.
• func() with parentheses calls the function and returns what it outputs

Question 12

Explain how the map function works

Answer 12

=> [4,5,6]

map returns a map object (an iterator) which can iterate over returned values from applying a function to every element in a sequence. The map object can also be converted to a list if required.

def add_three(x):
    return x+3

li = [1,2,3]

print(list(map(add_three, li)))

Question 13

Does python call by reference or call by value?

Answer 13

In a nutshell, all names call by reference, but some memory locations hold objects while others hold pointers to yet other memory locations.

Question 14

How to reverse a list?

Answer 14

li = [1,2,3,4]

li.reverse()

Question 15

How does the string multiplication work?

Answer 15

'cat'*3
#==> 'catcatcat'

Question 16

How does the list multiplication work?

Answer 16

[1,2,3]*2
#==> [1,2,3,1,2,3]

Question 16

How does the list multiplication work?

Answer 16

[1,2,3]*2
#==> [1,2,3,1,2,3]

Question 17

What does “self” refer to in a class?

Answer 17

• Self refers to the instance of the class itself

* give methods access to and the ability to update the object they belong to.

Question 18

How can you concatenate lists in python?

Answer 18

a = [1,2]
b = [3,4,5]

a+b
==> [1,2,3,4,5]

Question 19

What is the difference between lists and numpy arrays?

Answer 19

• Lists exist in python’s standard library. Arrays are defined by Numpy.
• Lists can be populated with different types of data at each index. Arrays require homogeneous elements.
• Arithmetic on lists adds or removes elements from the list. Arithmetic on arrays functions per linear algebra.
• Arrays also use less memory and come with significantly more functionality.

Question 20

how to concatenate numpy arrarys?

Answer 20

=> array([1,2,3,4,5,6])

import numpy as np
a = np.array([1,2,3])
b = np.array([4,5,6])

np.concatenate((a,b))

Question 21

What do you like about Python?

Answer 21

Python is very readable and there is a pythonic way to do just about everything, meaning a preferred way which is clear and concise.

I’d contrast this to Ruby where there are often many ways to do something without a guideline for which is preferred.

Question 22

What is you favorite library in Python?

Answer 22

When working with a lot data, nothing is quite as helpful as pandas which makes manipulating and visualizing data a breeze.

Question 23

Name mutable and immutable objects

Answer 23

• Immutable means the state cannot be modified after creation. Examples are: int, float, bool, string and tuple.
• Mutable means the state can be modified after creation. Examples are list, dict and set.

Question 24

Are dictionaries or lists faster for lookups?

Answer 24

• Looking up a value in a list takes O(n) time because the whole list needs to be iterated through until the value is found.
• Looking up a key in a dictionary takes O(1) time because it’s a hash table.
• This can make a huge time difference if there are a lot of values so dictionaries are generally recommended for speed. But they do have other limitations like needing unique keys.

Question 25

How to remove duplicate elements from a list?

Answer 25

=> [1,2,3]

a = [1,1,2,3,3,4]

print(list(set(a)))

Question 26

How can you sort a dictionary by key, alphabetically?

Answer 26

=>[(‘a’,1),(‘b’,2),(‘c’,3),(‘d’,4)]

You can’t “sort” a dictionary because dictionaries don’t have order but you can return a sorted list of tuples which has the keys and values that are in the dictionary.

d = {‘c’:3, ‘d’:4, ‘b’:2, ‘a’:4}

sorted(d.items())

Question 27

How to check string for numbers, letters, numbers and letters?

Answer 27

String.isnumeric()
String.isalpha()
String.isalnum()

Question 28

Return a list of keys from a dictionary.

Return a list of values from a dictionary.

Answer 28

> > > d = {‘a’:1,’b’:2,’d’:4,’c’:3}

> > > list(d)
[‘a’, ‘b’, ‘d’, ‘c’]

> > > list(d.keys()) # another way
[‘a’, ‘b’, ‘d’, ‘c’]

> > > list(d.values())
[1, 2, 4, 3]

Question 29

What is the difference between remove, del and pop?

Answer 29

remove() remove the first matching value.
del removes an element by index.
pop() removes an element by index and returns that element.

Question 30

How is exception handling performed in Python?

Answer 30

try: 
    try something
except:
    do something if failed
finally:
    do something else at the end always