The if, elif, and else Statements

This is the most fundamental conditional statement. It lets you execute a block of code only if a condition is true.

• if: Starts the block. The condition is evaluated. If True, the indented code under it runs.
• elif (short for "else if"): An optional block. If the first if is False, this condition is checked. You can have multiple elif blocks.
• else: An optional block that runs if all preceding if and elif conditions were False.

age = 18
has_permission = False
if age >= 18 and has_permission:
print("Access granted.")
elif age >= 18 and not has_permission:
print("You are old enough, but need permission.")
else:
print("Access denied. You are too young.")

Truthiness and Falsiness: In Python, it's not just True and False. Other values are considered "truthy" or "falsy" in a boolean context.

• Falsy values: False, None, zero of any numeric type (0, 0.0), and any empty sequence ("", [], ()) or collection ({}).
• Truthy values: Everything else! Any non-empty string, non-zero number, or non-empty collection is considered True.

The while Loop

The while loop executes a block of code as long as its condition remains true. It's ideal when you don't know in advance how many times you need to loop.

# Countdown from 5
count = 5
while count > 0:
    print(count)
    count -= 1 # This is crucial to avoid an infinite loop
print("Blast off!")

You can use break to exit a loop immediately and continue to skip the current iteration and jump to the top of the loop.

The for Loop

The for loop is used for iterating over a sequence (like a list, tuple, dictionary, set, or string). This is called a "for-each" loop in some other languages.

# Looping through a list
for fruit in ["apple", "banana", "cherry"]:
    print(f"I like {fruit}s")
Looping through a string
for char in "Python":
print(char, end='-') # P-y-t-h-o-n-

The range() function is a common partner for for loops. It generates a sequence of numbers.

• range(stop): Goes from 0 up to (but not including) stop.
• range(start, stop): Goes from start up to stop.
• range(start, stop, step): Goes from start to stop, incrementing by step.

Looping with else

A unique feature in Python is that loops can have an else block. This block executes only if the loop completes its entire sequence without being terminated by a break statement.

# Search for a number in a list
my_list = [1, 5, 9, 13]
search_for = 7
for num in my_list:
if num == search_for:
print("Found the number!")
break
else:
# This runs only if the loop finishes without a 'break'
print("The number was not in the list.")