Conditional Statements in Python

Conditional Statements in Python

What Are Conditional Statements?

• Control the flow of your program based on conditions.
• The most common statement is the if statement, which executes code only when a condition is true.
• Useful for decision-making in various applications, including NLP tasks.

Importance in NLP

• Adjust processing based on conditions (e.g., text case, keyword presence).
• Enable flexible and dynamic responses to input data.

word = "HELLO"
if word.isupper():
    print("The word is uppercase!")  # Output: The word is uppercase!

The word is uppercase!

The if Statement

Basic Syntax of if

• Check a condition and execute a block of code if it evaluates to True.

x = 10
if x > 5:
    print("x is greater than 5")  # Output: x is greater than 5

x is greater than 5

Explanation

• The condition x > 5 is checked.
• Since x is 10, the print statement executes.

The else Statement

Using the else Statement

• Defines what happens when the if condition is False.

x = 3
if x > 5:
    print("x is greater than 5")
else:
    print("x is not greater than 5")  # Output: x is not greater than 5

x is not greater than 5

Explanation

• Since x is 3, the else block executes, printing “x is not greater than 5”.

The elif Statement

Multiple Conditions with elif

• Use elif to check additional conditions if the previous ones are false.

x = 7
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")  # Output: x is greater than 5 but less than or equal to 10
else:
    print("x is less than or equal to 5")

x is greater than 5 but less than or equal to 10

Explanation

• Python checks each condition sequentially; x > 10 is false, but x > 5 is true.

Using Comparison Operators

Common Comparison Operators

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

age = 18
if age == 18:
    print("You are 18 years old")  # Output: You are 18 years old
if age != 20:
    print("You are not 20 years old")  # Output: You are not 20 years old

You are 18 years old
You are not 20 years old

Explanation

• The == operator checks if age is 18, while the != operator checks if it is not 20.

Logical Operators

Combining Conditions

• Use logical operators to evaluate multiple conditions.

x = 7

if x > 5 and x < 10:
    print("x is between 5 and 10")  # Output: x is between 5 and 10

x is between 5 and 10

Other Logical Operators

• or: True if at least one condition is true.
• not: Inverts the truth value of the condition.

if x < 5 or x > 6:
    print("x is either less than 5 or greater than 6")  # Output: x is either less than 5 or greater than 6

if not x == 5:
    print("x is not equal to 5")  # Output: x is not equal to 5

x is either less than 5 or greater than 6
x is not equal to 5

Nested if Statements

What Are Nested if Statements?

• Place one if statement inside another to check multiple conditions that depend on each other.

x = 10
y = 20

if x > 5:
    if y > 15:
        print("x is greater than 5 and y is greater than 15")  # Output: x is greater than 5 and y is greater than 15

x is greater than 5 and y is greater than 15

Explanation

• First check x > 5. If true, then check y > 15.

Checking Membership with in Operator

Using the in Operator

• Check if a value exists in a collection (e.g., list, string, tuple).

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

if "banana" in fruits:
    print("Banana is in the list!")  # Output: Banana is in the list!

Banana is in the list!

Example with Strings

sentence = "Hello world"
if "world" in sentence:
    print("The word 'world' is in the sentence.")  # Output: The word 'world' is in the sentence.

The word 'world' is in the sentence.

Combining Conditions in Practical Examples

Example: Password Validation

• Check user input against certain conditions for validity.

password = "Hello123"

if len(password) >= 8 and any(char.isdigit() for char in password):
    print("Password is valid")  # Output: Password is valid
else:
    print("Password must be at least 8 characters long and contain a number.")

Password is valid

Explanation

• Checks for length and if any character is a digit using char.isdigit().

Edge Cases and Handling Errors

Importance of Edge Case Handling

• Think about situations where input values might cause errors, such as empty strings or division by zero.

# Checking for division by zero
numerator = 10
denominator = 0

if denominator != 0:
    result = numerator / denominator
    print(result)
else:
    print("Cannot divide by zero")  # Output: Cannot divide by zero

Cannot divide by zero

Explanation

• Use conditionals to prevent errors like division by zero by checking if the denominator is not zero.