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Python Decision Making and Loops

Written by

Giga Alqeeq

in

Control Flow

Control Flow in Python refers to the order in which the statements and instructions in a Python program are executed. By default, Python executes code sequentially from top to bottom, but control flow structures allow you to make decisions, repeat actions, or change the execution path based on conditions. The main control flow tools in Python include:

Logical Expression

Logical Expression is a statement that can either be true or false. The following are some of the comparison operators:

1 > 2 is 1 bigger than 2 (Result is False)
1 < 2 is 1 smaller than 2 (Result is True)
1 == 2 is 1 equal to 2 (Result is False)
1 != 2 is 1 not equal to 2 (Result is True)
1 => 2 is 1 is equal or bigger than 2 (Result is False)
1 <= 2 is 1 is equal or smaller than 2 (Result is True)

Example

if 100 > 99: # Condition: if 100 is greater than 99 (True)
    print(“Good!”) # Since the condition is True, print “Good!”

if 100 > 99:
    print("Good!")

Result

Good!

Logical Operators

Logical Operators are used to connect\combine multiple logical expressions. The following are some of the logical operators:

1 == 1 and 2 == 2 is True because both statement are True
1 == 1 and 1 == 2 is False because only one statement is True
1 == 1 or 1 == 2 is True one of the statements is True
1 == 2 or 1 == 2 is False because neither statements is True

Example

if 100 > 99 and 99 == 99: # Both conditions must be True for the code inside to execute
    print(“Good!”) # Both conditions are True, so “Good!” is printed

if 100 > 99 and 99 == 99:
    print("Good!")

Result

Good!

if Statement

if keyword executes a block of code when a logical condition is met. if statement is one of the most well-known statement types. The if statement usually ends with :, and the block of code after the if a statement is indented.

Example

if 1 == 1: # Condition evaluates to True
    print(“Good!”) # Since the condition is True, print “Good!”

if 1 == 1:
    print("Good!")

Result

Good!

Or, you can do that without indentation

Example

if True: print(“Good!”)  # Condition evaluates to True, since the condition is True, print “Good!”

if True:print("Good!")

Result

Good!

if … elif Statement

if … elif keywords are used to check for multiple logical conditions.

Example

temp_value = 1 # Assign the value 1 to the variable temp_value
if temp_value == 1: # If temp_value equals 1
    print(“Value is 1”) # Print this message
elif temp_value == 2: # Otherwise, if temp_value equals 2
    print(“Value is 2”) # Print this message
elif temp_value == 3: # Otherwise, if temp_value equals 3
    print(“Value is 3”) # Print this message

temp_value = 1

if temp_value == 1:
    print("Value is 1")
elif temp_value == 2:
    print("Value is 2")
elif temp_value == 3:
    print("Value is 3")

Result

Value is 1

Now, change temp_value to 2 and try again

Example

temp_value = 2 # Assign the value 2 to the variable temp_value
if temp_value == 1: # If temp_value equals 1
    print(“Value is 1”) # Print this message
elif temp_value == 2: # Otherwise, if temp_value equals 2
    print(“Value is 2”) # Print this message
elif temp_value == 3: # Otherwise, if temp_value equals 3
    print(“Value is 3”) # Print this message

temp_value = 2

if temp_value == 1:
    print("Value is 1")
elif temp_value == 2:
    print("Value is 2")
elif temp_value == 3:
    print("Value is 3")

Result

Value is 2

if … else Statement

if … else keywords are used to check for one logical condition, if not, then execute the block of code after the else statement

Example

if 1 == 2: # Condition is False
    print(“Value is 1”) # This line is skipped because the condition is False
else: # Otherwise
    print(“Value is 2”) # Since the 1 == 2 condition is False, this line is executed

if 1 == 2:
    print("Value is 1")
else:
    print("Value is 2")

Result

Value is 2

for Statement

for keyword is used to iterate over a sequence (list, tuple, set, dict or, string) and executes a block of code every iteration. The for statement usually ends with :, and the block of code after the for a statement is indented.

Example

for item in range(5): # range(5) generates numbers 0,1,2,3,4
    print(item) # Print the current value of item in each iteration

for item in range(5):
    print(item)

Result

0
1
2
3
4

Or, you can do that without indentation

Example

for item in range(5):print(item) # range(5) generates numbers 0,1,2,3,4, then print the current value of item in each iteration

for item in range(5):print(item)

Result

0
1
2
3
4

while statement

while keyword is used to repeat executing a block of code as long as a condition is met. The while statement usually ends with :, and the block of code after the while a statement is indented.

Example

counter = 0 # Initialize a counter variable to 0
while counter < 5: # Continue looping while counter is less than 5
    print(counter, “is less than 5”) # Print the current value of counter and message
    counter = counter + 1 # Increment counter by 1 in each iteration

counter = 0

while counter < 5:
    print(counter, "is less than 5")
    counter = counter + 1

Result

0 is less than 5
1 is less than 5
2 is less than 5
3 is less than 5
4 is less than 5

break statement

break keyword is used to break for or while loop

Example

while True: # Start an infinite loop
    break # Immediately exit the loop
    print(“Looping…”) # This line will never run because break exits the loop first

while True:
    break
    print("Looping...")

Result

Nested statements

You can nest statements (Remember to indent when you nest)

Example

for item in range(5): # Loop through numbers from 0 to 4
    if item == 2: # Check if the current item equals 2
        print(“Item”, item, “Found!”) # Print the item 2
        print(“Breaking the loop”, item) # Print a message before breaking
        break # Exit the loop immediately

for item in range(5):
    if item == 2:
        print("Item", item, "Found!")
        print("Breaking the loop", item)
        break

Result

Item 2 Found!
Breaking the loop 2

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