100 Days Of Python - Day 2

Python - Day 2

Data Types

Data types are the building blocks of all languages. They are the different types of data that we can use in our programs.

Data types in Python include:

• String like “Hello World”
• Integer like 123 = All whole numbers positive and negative including 0 (without decimal point)
• Float like 3.14159
• Boolean like True or False
• List like [1, 2, 3]
• Dictionary like {‘name’: ‘Jack’, ‘age’: 23}
• Tuple like (1, 2, 3)
• Set like {1, 2, 3}
• None

String

Strings in Python are surrounded by either single quotation marks ' ', or double quotation marks " ".

print("Hello"[0]) # H
print("Hello"[4]) # o

Integer

Integers are used to store whole numbers. Integers are positive and negative numbers without decimals.

print(123 + 345) # 468
print(123_456_789) # 123456789

Float

Floats are used to store numbers with decimals.

print(3.14159) # 3.14159

Boolean

Booleans are used to store True or False values.

print(True) # True
print(False) # False

Type Error, Type Checking and Type Conversion

Type Error

If you try to combine a string with a number, Python will give you an error.

num_char = len(input("What is your name? "))
print("Your name has " + num_char + " characters.") # TypeError: can only concatenate str (not "int") to str

• TypeError: can only concatenate str (not "int") to str means that you can only concatenate strings to strings, not integers to strings.

Type Checking

You can check the type of a variable’s value using the type() function.

print(type(num_char)) # <class 'int'>

Type Conversion

You can convert one data type to another using the following functions:

• str() converts to string
• int() converts to integer
• float() converts to float

num_char = len(input("What is your name? ")) # this is an integer
# print("Your name has " + num_char + " characters.") # TypeError: can only concatenate str (not "int") to str
# we need to convert num_char to a string
new_num_char = str(num_char) # "50" this is a string
print("Your name has " + new_num_char + " characters.") # Your name has 50 characters.

Challenge

# Write a program that adds the digits in a 2 digit number. e.g. if the input was 35, then the output should be 3 + 5 = 8

# Warning. Do not change the code on lines 1-3. Your program should work for different inputs. e.g. any two-digit number.

# Example Input
two_digit_number = input("Type a two digit number: ")

print(type(two_digit_number)) # <class 'str'>
print(type(two_digit_number[0])) # <class 'str'>
print(type(two_digit_number[1])) # <class 'str'>
print(int(two_digit_number[0]) + int(two_digit_number[1])) # 8

# first_num = int(two_digit_number[0]);
# second_num = int(two_digit_number[1]);

# print(first_num + second_num)

Mathematical Operations in Python

print(3 + 5) # 8 - Addition
print(7 - 4) # 3 - Subtraction
print(3 * 2) # 6 - Multiplication
print(6 / 3) # 2.0 - Division
print(2 ** 3) # 8 - Exponent

PEMDAS (Order of Operations)

In Python, the order of operations is the same as in mathematics:

• Parentheses = ()
• Exponents = **
• Multiplication = *
• Division = /
• Addition = +
• Subtraction = -

print(3 * 3 + 3 / 3 - 3) # 7.0 - 3 * 3 = 9, 3 / 3 = 1, 9 + 1 = 10, 10 - 3 = 7
print(3 * (3 + 3) / 3 - 3) # 3.0 - 3 + 3 = 6, 3 * 6 = 18, 18 / 3 = 6, 6 - 3 = 3

BMI Calculator

Instructions:

• Write a program that calculates the Body Mass Index (BMI) from a user’s weight and height.
• The BMI is a measure of some’s weight taking into account their height. e.g. If a tall person and a short person both weigh the same amount, the short person is usually more overweight.
• The BMI is calculated by dividing a person’s weight (in kg) by the square of their height (in m):
• Warning you should convert the result to a whole number.

Example Input

• weight = 80
• height = 1.75

Example Output

• 80 ÷ (1.75 x 1.75) = 26

Hint

1. Check the data type of the inputs.
2. Try to use the exponent operator in your code.
3. Remember PEMDAS.
4. Remember to convert your result to a whole number (int).

Solution

height = input("enter your height in m: ")
weight = input("enter your weight in kg: ")

print(type(height)) # <class 'str'>
print(type(weight)) # <class 'str'>

bmi = int(weight) / float(height) ** 2
print(int(bmi)) # 26

Number Manipulation and F Strings in Python

In python, you can use

• the round() function to round a number to a certain number of decimal places.

print(round(8 / 3)) # 3
print(round(8 / 3, 2)) # 2.67 - round to 2 decimal places
print(round(8 / 3, 3)) # 2.667 - round to 3 decimal places

• the // operator to get the integer part of a division

print(8 // 3) # 2

• the % operator to get the remainder of a division

print(8 % 3) # 2

F-Strings

• F-Strings are a new way to format strings in Python 3.6 and above.
• They allow you to put variables inside a string.
• You can use f-strings by putting an f before the opening quote of a string.
• Then you can put variables inside the string by using curly braces {}.

score = 0
height = 1.8
isWinning = True

# f-String
print(f"your score is {score}, your height is {height}, you are winning is {isWinning}") # your score is 0, your height is 1.8, you are winning is True

Life in Weeks

Instructions

• Create a program using maths and f-Strings that tells us how many days, weeks, months we have left if we live until 90 years old.
• It will take your current age as the input and output a message with our time left in this format:

You have x days, y weeks, and z months left. Where x, y and z are replaced with the actual calculated numbers.

Hint

1. There are 365 days in a year, 52 weeks in a year and 12 months in a year.
2. Try copying the example output into your code and replace the relevant parts so that the sentence is formated the same way.
3. Remember to use the round() function to round the final number of days, weeks and months. Note that the round() function will convert the float into an integer. Hint You will need to Google how to convert a float into an integer.
4. Your life span in years is calculated from your current age and the number 90.
5. Try running your code for different ages to calculate the number of days, weeks and months you have left to live.
6. Bonus: Format the numbers so that the output looks nicer. Hint: You will need to Google how to use the f"{value:2d}" syntax.

Solution

age = input("What is your current age? ")

years_left = 90 - int(age)
days_left = years_left * 365
weeks_left = years_left * 52
months_left = years_left * 12

message = f"You have {days_left} days, {weeks_left} weeks, and {months_left} months left."
print(message)

Tip Calculator

Instructions

• If the bill was $150.00, split between 5 people, with 12% tip.
• Each person should pay (150.00 / 5) * 1.12 = 33.6
• Format the result to 2 decimal places = 33.60
• Tip: There are 2 ways to round a number. You might have to do some Googling to solve this.💪

Hint

1. Try to print the result of the division.
2. Try to print the result of the multiplication.
3. Try to print the result of the division.
4. Try to print the result of the multiplication.

Solution

print("Welcome to the tip calculator.")
total_bill = float(input("What was the total bill? $"))
tip_percentage = int(input("What percentage tip would you like to give? 10, 12, or 15? "))
number_of_people = int(input("How many people to split the bill? "))
bill_with_tip = total_bill * (1 + tip_percentage / 100)
bill_per_person = bill_with_tip / number_of_people
#final_amount = round(bill_per_person, 2) # round to 2 decimal places
final_amount = "{:.2f}".format(bill_per_person) # round to 2 decimal places

print(f"Each person should pay: ${final_amount}")