python coding notes

Question 1

how to find where a character is

Answer 1

.index(character)

Question 2

how to remove something from a list

Answer 2

list.pop(position of char)

Question 3

different ways to show range

Answer 3

• for i in range
• num for num

Question 4

different ways to do loops

Answer 4

• for i in
• char for char

Question 5

how to find the number of time something occurs in a list

Answer 5

.occur()

Question 6

how to sort list

Answer 6

• sorted(list)
• list.sort()

Question 7

how to find length of something

Answer 7

len()

Question 8

how to insert an element into a specific index of a list

Answer 8

list.insert()

Question 9

how to skip numbers when doing range

Answer 9

• add a third input, eg range(2,9,2) would output 2,4,6,8

Question 10

how to slice lists

Answer 10

list[start:end]

Question 11

how to see how many times an element occurs in a string or list

Answer 11

.count

Question 12

how to remove duplicates in a list

Answer 12

use list(set())

Question 13

what is a tuple

Answer 13

a data structure that allows us to store multiple pieces of data inside of it
- the elements, the order of the elements and how many elements there are cannot be changed
- they are immutable, can’t be edited

Question 14

what does zip() do

Answer 14

takes two or more list as inputs and returns an object that contains a list of pairs. each pair contains one element from each of the inputs

Question 15

what is indefinite iteration

Answer 15

where the number of times the loop is executed depends on how many times a condition is met

Question 16

what is definite iteration

Answer 16

where the number of times the loop will be executed is defined in advance

Question 17

what does a while loop do

Answer 17

performs a set of instructions as long as a given condition is true

Question 18

what does break do

Answer 18

stops an iteration

Question 19

how to carry on an iteration

Answer 19

continue

Question 20

how to iterate using a list

Answer 20

[(what u wanna append to the list) for i in list]

Question 21

string in built functions

Answer 21

.strip() - removes characters from string
- .find() - finds the position of a character in a string

Question 22

how to reverse a list

Answer 22

• list.reverse()
• Reverse = True
• [::-1]

Question 23

what does enumerate do()

Answer 23

generates tuples which represent the indices and values of the elements in the list

Question 24

what does while True do

Answer 24

loops forever

Question 25

what does try do

Answer 25

lets you test a block of code for errors.

Question 26

how to check if something is a digit

Answer 26

.isdigit()

Question 27

how to repeat a loop, for example in a game

Answer 27

use While True

Question 28

difference between pop and remove

Answer 28

remove removes using values pop removes using indexes

Question 29

if string.strip() what does this mean

Answer 29

checks if the input string is not empty after removing leading and trailing whitespace

Question 30

other ways to remove white space in sentence

Answer 30

- “”.join(sentence.split()) - sentence.replace(“ “, “”)

Question 31

what else does list()

Answer 31

- converts a string into a list, where each character in the string is a separate element in the list - eg hello is [“h”, “e”, “l”, “l”,”o”]

Question 32

what does zip do

Answer 32

used to combine two or more iterables, eg an integer and string, or string and a list - eg - for i,j in zip(str(n)), range(1,len(str(n))+1) , this combines a string and an integer

Question 33

how to do square root

Answer 33

math.sqrt() but import math before u do this

Question 34

how to check if a number is whole

Answer 34

mod it by 1

Question 35

how to make a number whole

Answer 35

round()

Question 36

what does abs() do

Answer 36

gives the absolute value of a number, - turns negative numbers positive, eg -5 to 5 - leaves positive numbers unchanged

Question 37

what does set() do

Answer 37

A set automatically removes duplicate elements. Each element in a set must be unique. Sets do not maintain any specific order of elements. you can add or remove elements after the set has been created.

Question 38

how to find the position of a character in a string/list

Answer 38

use variablename.index(character) - eg. if theres a string called letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" and you want to find where X is: for char in userInput: if char in letters: current_index = letters.index(char)

Question 39

when to use try and except

Answer 39

The try and except block is used to handle situations where the user inputs something invalid (like entering letters instead of a number) 1. Handling User Input Errors When converting user input into a specific data type, errors may occur if the input is invalid. eg. try: age = int(input("Enter your age: ")) except ValueError: print("Invalid input! Please enter a number.")

Question 40

when to use a for loop

Answer 40

You Want to Continuously Prompt the User Until Valid Input Is Provided: For example, asking a user for a valid number or email address until they provide one. Loops make it easy to repeat the request. You Need Custom Validation Logic: For example: - Checking if a string contains only specific characters. - Ensuring input meets specific constraints (e.g., a number in a range). - A loop allows you to write your own logic instead of relying solely on Python’s built-in exception system. Errors Are Not Easily Capturable by Exceptions: - For example, checking if a string contains only letters is not something that throws an exception—you need to check this explicitly using string methods. You Want More Granular Feedback: - If you want to inform the user why their input is invalid (e.g., "Value is too large" or "Must be a number"), loops can provide more flexibility.

Question 41

how to do a factorial recursion function

Answer 41

def factorial(x): if x == 1: return 1 else: return x * factorial(x -1)

Question 42

how to check if any character in an input is a digit

Answer 42

if not any(char.isdigit() for char in userInput):

Question 43

Write a function that sorts a list of numbers based on the sum of their digits in descending order. - The function should return the sorted list.

Answer 43

def sum_digits(x): count = 0 for i in str(x): count+= int(i) return count def digit_sum_sort(inputList): newList = [] for i in inputList: newList.append((i, sum_digits(i))) newList.sort(key=lambda item : (item[1], item[1]), reverse=True) sortedList = [item[0] for item in newList] return sortedList print(digit_sum_sort([134, 23, 45, 98, 321, 500]))

Question 44

how to sort a parts of a tuple in descending order

Answer 44

newList.sort(key=lambda item : (item[1], item[1]), reverse=True) sortedList = [item[0] for item in newList]

Question 45

when to use while True opposed to while(a condition)

Answer 45

Use while True when: - You don’t know beforehand when the loop will stop - eg: Finding the smallest multiple (we don’t know the number in advance) - You want to keep asking for user input until they enter valid data -eg: Keep asking for a number until the user enters a valid one. Use while (a condition) when: - You know the stopping condition in advance eg: Count down from 10 to 1 - You have a specific range or limit eg: Running a loop only if a number is less than 50. python Copy Edit

Question 46

how to convert digit to a list

Answer 46

list(map(int, str(n)))

Question 47

how to copy a list

Answer 47

newlist=list**[:]**

Question 48

how to use a global variable

Answer 48

- define it before ALL the functions - do not include it in a functions parameters. Instead, say the global variable in the first line of the function

Question 49

difference between break and continue

Answer 49

break stops a loop once its condition is met, while continue skips over the current iteration of a loop and continues to the next iteration based on its condition.