Python in 30 Days: Day 3 – Operators
Day 3
Boolean
A boolean data type represents one of the two values: True or False. The use of these data types will be clear once we start using the comparison operator. The first letter T for True and F for False should be capital, unlike in JavaScript. Example: Boolean Values
print(True)
print(False)
Operators
Python language supports several types of operators. In this section, we will focus on a few of them.
Assignment Operators
Assignment operators are used to assign values to variables. Let us take = as an example. An equal sign in mathematics shows that two values are equal, however in Python, it means we are storing a value in a certain variable and we call it an assignment or assigning value to a variable. The table below shows the different types of Python assignment operators, taken from w3school.
Arithmetic Operators:
- Addition(+): a + b
- Subtraction(-): a – b
- Multiplication(*): a * b
- Division(/): a / b
- Modulus(%): a % b
- Floor division(//): a // b
- Exponentiation(**): a ** b
Example: Integers
# Arithmetic Operations in Python
# Integers
print('Addition: ', 1 + 2) # 3
print('Subtraction: ', 2 - 1) # 1
print('Multiplication: ', 2 * 3) # 6
print ('Division: ', 4 / 2) # 2.0 Division in Python gives floating number
print('Division: ', 6 / 2) # 3.0
print('Division: ', 7 / 2) # 3.5
print('Division without the remainder: ', 7 // 2) # 3, gives without the floating number or without the remaining
print ('Division without the remainder: ',7 // 3) # 2
print('Modulus: ', 3 % 2) # 1, Gives the remainder
print('Exponentiation: ', 2 ** 3) # 9 it means 2 * 2 * 2
Example: Floats
# Floating numbers
print('Floating Point Number, PI', 3.14)
print('Floating Point Number, gravity', 9.81)
Example: Complex numbers
# Complex numbers
print('Complex number: ', 1 + 1j)
print('Multiplying complex numbers: ',(1 + 1j) * (1 - 1j))
Let’s declare a variable and assign a number data type. I am going to use single character variable but remember do not develop a habit of declaring such types of variables. Variable names should be all the time mnemonic.
Example:
# Declaring the variable at the top first
a = 3 # a is a variable name and 3 is an integer data type
b = 2 # b is a variable name and 3 is an integer data type
# Arithmetic operations and assigning the result to a variable
total = a + b
diff = a - b
product = a * b
division = a / b
remainder = a % b
floor_division = a // b
exponential = a ** b
# I should have used sum instead of total but sum is a built-in function - try to avoid overriding built-in functions
print(total) # if you do not label your print with some string, you never know where the result is coming from
print('a + b = ', total)
print('a - b = ', diff)
print('a * b = ', product)
print('a / b = ', division)
print('a % b = ', remainder)
print('a // b = ', floor_division)
print('a ** b = ', exponentiation)
Example:
print('== Addition, Subtraction, Multiplication, Division, Modulus ==')
# Declaring values and organizing them together
num_one = 3
num_two = 4
# Arithmetic operations
total = num_one + num_two
diff = num_two - num_one
product = num_one * num_two
div = num_two / num_one
remainder = num_two % num_one
# Printing values with label
print('total: ', total)
print('difference: ', diff)
print('product: ', product)
print('division: ', div)
print('remainder: ', remainder)
Let us start connecting the dots and start making use of what we already know to calculate (area, volume, density, weight, perimeter, distance, force).
Example:
# Calculating area of a circle
radius = 10 # radius of a circle
area_of_circle = 3.14 * radius ** 2 # two * sign means exponent or power
print('Area of a circle:', area_of_circle)
# Calculating area of a rectangle
length = 10
width = 20
area_of_rectangle = length * width
print('Area of rectangle:', area_of_rectangle)
# Calculating a weight of an object
mass = 75
gravity = 9.81
weight = mass * gravity
print(weight, 'N') # Adding unit to the weight
# Calculate the density of a liquid
mass = 75 # in Kg
volume = 0.075 # in cubic meter
density = mass / volume # 1000 Kg/m^3
Comparison Operators
In programming we compare values, we use comparison operators to compare two values. We check if a value is greater or less or equal to another value. The following table shows Python comparison operators which were taken from w3shool.
Example: Comparison Operators
print(3 > 2) # True, because 3 is greater than 2
print(3 >= 2) # True, because 3 is greater than 2
print(3 < 2) # False, because 3 is greater than 2
print(2 < 3) # True, because 2 is less than 3
print(2 <= 3) # True, because 2 is less than 3
print(3 == 2) # False, because 3 is not equal to 2
print(3 != 2) # True, because 3 is not equal to 2
print(len('mango') == len('avocado')) # False
print(len('mango') != len('avocado')) # True
print(len('mango') < len('avocado')) # True
print(len('milk') != len('meat')) # False
print(len('milk') == len('meat')) # True
print(len('tomato') == len('potato')) # True
print(len('python') > len('dragon')) # False
# Comparing something gives either a True or False
print('True == True: ', True == True)
print('True == False: ', True == False)
print('False == False:', False == False)
In addition to the above comparison operator Python uses:
- is: Returns true if both variables are the same object(x is y)
- is not: Returns true if both variables are not the same object(x is not y)
- in: Returns True if the queried list contains a certain item(x in y)
- not in: Returns True if the queried list doesn’t have a certain item(x in y)
print('1 is 1', 1 is 1) # True - because the data values are the same
print('1 is not 2', 1 is not 2) # True - because 1 is not 2
print('A in Asabeneh', 'A' in 'Asabeneh') # True - A found in the string
print('B in Asabeneh', 'B' in 'Asabeneh') # False - there is no uppercase B
print('coding' in 'coding for all') # True - because coding for all has the word coding
print('a in an:', 'a' in 'an') # True
print('4 is 2 ** 2:', 4 is 2 ** 2) # True
Logical Operators
Unlike other programming languages python uses keywords and, or and not for logical operators. Logical operators are used to combine conditional statements:
print(3 > 2 and 4 > 3) # True - because both statements are true
print(3 > 2 and 4 < 3) # False - because the second statement is false
print(3 < 2 and 4 < 3) # False - because both statements are false
print('True and True: ', True and True)
print(3 > 2 or 4 > 3) # True - because both statements are true
print(3 > 2 or 4 < 3) # True - because one of the statements is true
print(3 < 2 or 4 < 3) # False - because both statements are false
print('True or False:', True or False)
print(not 3 > 2) # False - because 3 > 2 is true, then not True gives False
print(not True) # False - Negation, the not operator turns true to false
print(not False) # True
print(not not True) # True
print(not not False) # False
Now do some exercises for your brain and your muscles.
Exercises – Day 3
- Declare your age as an integer variable
- Declare your height as a float variable
- Declare a variable that stores a complex number
- Write a script that prompts the user to enter the base and height of the triangle and calculate the area of this triangle (area = 0.5 x b x h).
Enter base: 20
Enter height: 10
The area of the triangle is 100
- Write a script that prompts the user to enter side a, side b, and side c of the triangle. Calculate the perimeter of the triangle (perimeter = a + b + c).
Enter side a: 5
Enter side b: 4
Enter side c: 3
The perimeter of the triangle is 12
- Get the length and width of a rectangle using the prompt. Calculate its area (area = length x width) and perimeter (perimeter = 2 x (length + width))
- Get the radius of a circle using the prompt. Calculate the area (area = pi x r x r) and circumference (c = 2 x pi x r) where pi = 3.14.
- Calculate the slope, x-intercept, and y-intercept of y = 2x -2
- Slope is (m = y2-y1/x2-x1). Find the slope and Euclidean distance between point (2, 2) and point (6,10)
- Compare the slopes in tasks 8 and 9.
- Calculate the value of y (y = x^2 + 6x + 9). Try to use different x values and figure out at what x value y is going to be 0.
- Find the length of ‘python’ and ‘dragon’ and make a falsy comparison statement.
- Use an operator to check if ‘on’ is found in both ‘python’ and ‘dragon’
- I hope this course is not full of jargon. Use in operator to check if jargon is in the sentence.
- There is no ‘on’ in both dragon and python
- Find the length of the text Python converts the value to float and converts it to string
- Even numbers are divisible by 2 and the remainder is zero. How do you check if a number is even or not using Python?
- Check if the floor division of 7 by 3 is equal to the int converted value of 2.7.
- Check if the type of ’10’ is equal to the type of 10
- Check if int(‘9.8’) is equal to 10
- Write a script that prompts the user to enter hours and rate per hour. Calculate the pay of the person.
Enter hours: 40
Enter rate per hour: 28
Your weekly earning is 1120
- Write a script that prompts the user to enter a number of years. Calculate the number of seconds a person can live. Assume a person can live a hundred years
Enter number of years you have lived: 100
You have lived for 3153600000 seconds.
- Write a Python script that displays the following table
1 1 1 1 1
2 1 2 4 8
3 1 3 9 27
4 1 4 16 64
5 1 5 25 125
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