Conditionals and loops

In Python, conditionals and loops are fundamental constructs that control the flow of a program.

Boolean conditions

In Python, a condition is an expression that evaluates to either True or False. Conditions are used to make decisions in the code, such as whether to execute a certain block of code, repeat a loop, or choose between different options.

Common Conditional Expressions

Here are some common ways to create conditions in Python.

Comparison Operators

These operators compare two values and return True or False.

== : Equal to
!= : Not equal to
> : Greater than
< : Less than
>= : Greater than or equal to
<= : Less than or equal to

x = 10
y = 5
condition = (x > y)  # True, because 10 is greater than 5

Logical Operators

These operators are used to combine multiple conditions.

and : Returns True if both conditions are True
or : Returns True if at least one condition is True
not : Returns True if the condition is False

x = 10
y = 5
z = 3
condition = ((x > y) and (y > z))  # True, because both x > y and y > z are True

Membership Operators

These operators are used to check if a value is in a sequence (like a list, tuple, or string).

in : Returns True if the value is found in the sequence
not in : Returns True if the value is not found in the sequence

numbers = [1, 2, 3, 4, 5]
condition = (3 in numbers)  # True, because 3 is in the list

Identity Operators

These operators compare the memory locations of two objects.

is : Returns True if both variables point to the same object
is not : Returns True if the variables point to different objects

a = [1, 2, 3]
b = a
condition = (a is b)  # True, because b refers to the same object as a

Conditionals

Conditionals are used to execute certain pieces of code based on whether a condition is True or False. Python provides if, elif, and else statements for conditional execution.

if condition1:
        # code block to execute if condition1 is True
elif condition2:
        # code block to execute if condition2 is True
else:
        # code block to execute if none of the above conditions are True

For example:

if x > 10:
        print("x is greater than 10")
elif x > 5:
        print("x is greater than 5 but less than or equal to 10")
else:
        print("x is 5 or less")

If you test this code for x = 7, the result is : "x is greater than 5 but less than or equal to 10".

Loops

Loops are used to repeatedly execute a block of code as long as a condition is true or for a specified number of iterations.

for Loop

A for loop is used to iterate over a sequence (such as a list, tuple, dictionary, set, or string).

for item in sequence:
        # code block to execute for each item in the sequence

For example:

numbers = [1, 2, 3, 4, 5]
for number in numbers:
        print(number)

This example give this output:

range() with for Loop

The range() function generates a sequence of numbers, which is often used with a for loop.

for i in range(start, stop, step):
        # code block to execute for each value in the range

For example:

for i in range(1, 6):
        print(i)

This example give this output:

enumerate() with for Loop

When you use enumerate() in a for loop, it provides two values: the index (which starts from 0 by default) and the item from the iterable. This is particularly useful when you need both the element and its position in the iterable.

for index, item in enumerate(iterable, start=0):
        # Code block that uses index and item

`iterable`: The sequence you want to loop over (e.g., a list, tuple, string).
`start`: The index value at which to start counting (default is 0).

Example with a List:

fruits = ["apple", "banana", "cherry"]

for index, fruit in enumerate(fruits):
        print(f"Index: {index}, Fruit: {fruit}")

This example give this output:

Index: 0, Fruit: apple
Index: 1, Fruit: banana
Index: 2, Fruit: cherry

while Loop

A while loop repeatedly executes a block of code as long as the condition is True.

while condition:
        # code block to execute while the condition is True

x = 1
while x <= 5:
        print(x)
        x += 1

This example give this output:

break and continue

`break`: Exits the loop prematurely, regardless of the loop’s condition.
`continue`: Skips the rest of the current iteration and moves on to the next iteration.

Example using break:

for i in range(1, 10):
        if i == 5:
                break
        print(i)

This example give this output:

Example using continue:

for i in range(1, 6):
        if i == 3:
                continue
        print(i)

This example give this output: