Introduction to Python

Question 1

What is Print?

Answer 1

print () - built-in function that displays input values as text in the output

Question 2

What are Arithmetic operators?

Answer 2

Arithmetic Operators

+ Addition
- Subtraction
* Multiplication
/ Division
% Mod (the remainder after dividing)
** Exponentiation (note that ^ does not do this operation, as you might have seen in other languages)
// Divides and rounds down to the nearest integer

Question 3

What is PEDMAS?

Answer 3

PEMDAS: Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.

Question 4

What is the type function?

Answer 4

it can be used to check the data type of any variable you are working with.

Question 5

what is len() function?

Answer 5

len() is a built-in Python function that returns the length of an object, like a string. The length of a string is the number of characters in the string. This will always be an integer.

Question 6

what are String Methods?

Answer 6

len(“this”)
type(12)
print(“Hello world”)
sample_string.lower()
my_string.islower() - does not accept another argument.
my_string.count(‘a’)
my_string.find(‘a’) - both take another argument
print(“Mohammed has {} balloons”.format(27)
print(“Does your {} {}?”.format(animal, action))

Question 7

what is F-String Formatting?

Answer 7

F-strings provide a concise and convenient way to embed expressions inside string literals, using curly brackets {}. The expressions will be replaced with their values when the string is evaluated.
a = 5
b = 3
print(f”The sum of {a} and {b} is {a+b}”)

name = “John”
print(f”Hello, {name}”)

Question 8

What is String Method - Split?

Answer 8

The split method has two arguments (sep and maxsplit).
The sep argument stands for “separator”. It can be used to identify how the string should be split up (e.g., whitespace characters like space, tab, return, newline; specific punctuation (e.g., comma, dashes)).
If the sep argument is not provided, the default separator is whitespace.

True to its name, the maxsplit argument provides the maximum number of splits. The argument gives maxsplit + 1 number of elements in the new list, with the remaining string being returned as the last element in the list.

Question 9

Examples for split method

Answer 9

new_str = “The cow jumped over the moon.”
new_str.split()
[‘The’, ‘cow’, ‘jumped’, ‘over’, ‘the’, ‘moon.’]

new_str.split(‘ ‘, 3)
[‘The’, ‘cow’, ‘jumped’, ‘over the moon.’]

new_str.split(‘.’)
[‘The cow jumped over the moon’, ‘’]

new_str.split(None, 3)

[‘The’, ‘cow’, ‘jumped’, ‘over the moon.’]

Question 10

How do you find the length, first, last and count occurrence of word from string?

Answer 10

length = len(verse)
first_idx = verse.find(‘and’)
last_idx = verse.rfind(‘you’)
count = verse.count(‘you’)

Question 11

What Are Data Structures?

Answer 11

Data structures are containers or collections of data that organize and group data types together in different ways. You can think of data structures as file folders that have organized files of data inside them.

Question 12

What are Lists?

Answer 12

list is one of the most common and basic data structures in Python.

Question 13

How do you create List?

Answer 13

create a list with square brackets.

Lists can contain any mix and match of the data types you have seen so far.

list_of_random_things = [1, 3.4, ‘a string’, True]

Question 14

Are lists Ordered?

Answer 14

Yes

Question 15

Are lists Mutable?

Answer 15

Yes

Question 16

Slice and Dice with Lists?

Answer 16

using slicing, it is important to remember that
the lower index is inclusive and
the upper index is exclusive

This type of indexing works exactly the same on strings, where the returned value will be a string.

Question 17

What are Membership Operators?

Answer 17

in ==> evaluates if an element exists within our list
not in ==> evaluates if an element does not exist within our list

> > > 5 not in [1, 2, 3, 4, 6]
True
5 in [1, 2, 3, 4, 6]
False

Question 18

Mutability?

Answer 18

Mutability refers to whether or not we can change an object once it has been created. If an object can be changed, it is called mutable. However, if an object cannot be changed after it has been created, then the object is considered immutable.

Examples - Lists are mutable, and strings are immutable.

Question 19

Ordered?

Answer 19

Order is about whether the position of an element in the object can be used to access the element. Both strings and lists are ordered. We can use the order to access parts of a list and string.

Question 20

Useful Functions for Lists?

Answer 20

len() returns how many elements are in a list.
max() returns the greatest element of the list.
max() function is undefined for lists that contain elements from different, incomparable types.
min() returns the smallest element in a list.
sorted() returns a copy of a list in order from smallest to largest, leaving the list unchanged.
append method
A helpful method called append adds an element to the end of a list.

Question 21

What is join method in List

Answer 21

Join is a string method that takes a list of strings as an argument, and returns a string consisting of the list elements joined by a separator string.

new_str = “\n”.join([“fore”, “aft”, “starboard”, “port”])
print(new_str)
Output:
fore
aft
starboard
port

name = “-“.join([“García”, “O’Kelly”, “Davis”])
print(name)
Output:
García-O’Kelly-Davis

Question 22

What are Tuples?

Answer 22

A tuple is another useful container. It’s a data type for immutable ordered sequences of elements. They are often used to store related pieces of information.

Question 23

How Tuples can be created?

Answer 23

Tupes can be created using brackets ()
location = (13.4125, 103.866667)
The parentheses are optional when defining tuples, and programmers frequently omit them if parentheses don’t clarify the code.
dimensions = 52, 40, 100

Question 24

How Tuples are accessed?

Answer 24

Tuples are similar to lists in that they store an ordered collection of objects which can be accessed by their indices.

Question 25

Are Tuples mutable?

Answer 25

tuples are immutable - you can’t add and remove items from tuples, or sort them in place.

Question 26

what is tuple unpacking?

Answer 26

dimensions = 52, 40, 100
length, width, height = dimensions
print(“The dimensions are {} x {} x {}”.format(length, width, height))

In the second line, three variables are assigned from the content of the tuple dimensions. This is called tuple unpacking. You can use tuple unpacking to assign the information from a tuple into multiple variables without having to access them one by one and make multiple assignment statements.

Question 27

What are Sets?

Answer 27

A set is a data type for mutable unordered collections of unique elements.

Question 28

Does set has duplicate elements?

Answer 28

No
numbers = [99, 100, 1, 3, 4, 99, 100]
unique_nums = set(numbers)
print(unique_nums)

Output
{1, 3, 99, 100, 4}

Question 29

How a set is defined?

Answer 29

using curly braces { }

Question 30

What are methods in sets?

Answer 30

add elements to sets using the add method, remove elements using the pop method
Note: pop an element from a set, a random element is removed.

Question 31

are set is ordered?

Answer 31

No Set is unordered.

Question 32

How do you perform union on list or set?

Answer 32

Sample data
set1 = set(range(1000))
set2 = set(range(500, 1500))
list1 = list(set1)
list2 = list(set2)

Union
start_time = time.time()
union_set = set1.union(set2)

start_time = time.time()
union_list = list(set(list1 + list2))

Question 33

How do you perform Intersection on sets and lists?

Answer 33

intersection_set = set1.intersection(set2)

intersection_list = [x for x in list1 if x in set2]

Question 34

How do you find difference on set or lists?

Answer 34

difference_set = set1.difference(set2)

difference_list = [x for x in list1 if x not in set2]

Question 35

operations performed on set objects are significantly faster than those on list objects?

Answer 35

Yes.

Question 36

what are dictionaries?

Answer 36

A dictionary is a mutable data type that stores mappings of unique keys to values.

In general, dictionaries look like key-value pairs, separated by commas:

{key1:value1, key2:value2, key3:value3, key4:value4, …}

Question 37

How dictionaries are created?

Answer 37

Using curly braces { }

Question 38

In python does only dictionaries are created using the curly braces?

Answer 38

No.
Both Set and dictionaries are created using the same curly braces { }

Question 39

Are dictionaries mutable?

Answer 39

Yes.
Key part is immutable.
Value part is mutable.

Question 40

How can we access the dictionary elements?

Answer 40

Using the key value passed using the Square brackets
elements = {“hydrogen”: 1, “helium”: 2, “carbon”: 6}
print(elements[“helium”])
Alternatively,
print(elements.get(“helium”))
unlike square brackets will give you a “KeyError”, get returns None (or a default value of your choice) if the key isn’t found.

Question 41

Can we use in and not in for dictionaries elements?

Answer 41

Yes.

print(“carbon” in elements)

Question 42

what are Identity Operators?

Answer 42

is ==> evaluates if both sides have the same identity
is not ==> evaluates if both sides have different identities

n = elements.get(“dilithium”)
print(n is None)
print(n is not None)

output:
True
False

Question 43

what are Compound Data Structures?

Answer 43

include containers in other containers to create compound data structures. For example, this dictionary maps keys to values that are also dictionaries!

We can access elements in this nested dictionary like this.

Question 44

What is zip?

Answer 44

zip returns an iterator that combines multiple iterables into one sequence of tuples. Each tuple contains the elements in that position from all the iterables.
For example, printing

list(zip([‘a’, ‘b’, ‘c’],
[1, 2, 3]))
would output
[(‘a’, 1), (‘b’, 2), (‘c’, 3)].

for letter, num in zip(letters, nums):
print(“{}: {}”.format(letter, num))

Question 45

what is unzipping?

Answer 45

exactly opposite of zip.
unzip a list into tuples using an asterisk.

some_list =
[(‘a’, 1), (‘b’, 2), (‘c’, 3)]
letters, nums = zip(*some_list)

Question 46

what is enumerate?

Answer 46

enumerate is a built in function that returns an iterator of tuples containing indices and values of a list. You’ll often use this when you want the index along with each element of an iterable in a loop.

letters =
[‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
for i, letter in enumerate(letters):
print(i, letter)
output:
0 a
1 b
2 c
3 d
4 e

Question 47

what is List Comprehensions?

Answer 47

List comprehensions allow us to create a list using a for loop in one step.

You create a list comprehension with brackets [].

Question 48

How the list comprehension works?

Answer 48

capitalized_cities = []
for city in cities: capitalized_cities.append(city.title())

can be reduced to:
capitalized_cities = [city.title() for city in cities]

Question 49

Can we use Conditionals in List Comprehensions?

Answer 49

After the iterable, you can use the if keyword to check a condition in each iteration.

squares = [x**2 for x in range(9) if x % 2 == 0] sets squares equal to the list [0, 4, 16, 36, 64], as x to the power of 2 is only evaluated if x is even.
==> Here if acts as a filter of the for-loop.

If you would like to add else, you have to move the conditionals to the beginning of the listcomp, right after the expression, like this.

squares = [x**2 if x % 2 == 0 else x + 3 for x in range(9)]

==> Here if acts as a conditional expression of the for-loop.