Conditions are expressions that evaluate to True or False, allowing your code to make decisions and execute different actions based on those evaluations. They are essential for creating programs responding to various inputs and scenarios.
The condition can be any logical expression formed using:
Used to compare values:
== (equal to)
!= (not equal to)
< (less than)
> (greater than)
<= (less than or equal to) = (greater than or equal to)
Example: if age >= 18:
Combine multiple conditions:
and (both conditions must be True)
or (at least one condition must be True)
not (inverts the truth value of a condition)
Example: if grade == “A” or grade == “B”:
These check if an element is present in a sequence. Examples include in (checks if an element is in a list) and not in (checks if an element is not in a list).
These can be more complex combinations of the above elements.
Check all Python operators here
The “if” statement, in any programming language including Python, plays a crucial role in controlling the flow of your program. It lets you make decisions based on certain conditions.
Here's a comprehensive breakdown of the “if” statement:
Execute code only if a condition is True.
if condition:
# Code to execute if the condition is True
# Example:
if temperature > 40:
print("It's a hot day!")
if condition: This is the heart of the statement. It's a logical expression that evaluates to True or False.
Code to execute: These are the statements that will be executed if the condition is True (within the if block) or False (within the else block). The else block is optional.
Indentation:
Python uses indentation to define code blocks. Consistent indentation (usually 4 spaces) is crucial for readability and syntax.
Like in the above example you can see there is space in the print statement.
Allow checking multiple conditions sequentially and execute code only if the previous conditions were False.
if condition1:
# Code to execute if condition1 is True
elif condition2:
# Code to execute if condition1 is False and condition2 is True
# Example:
grade = input("Enter your grade: ")
if grade == "A":
print("Excellent!")
elif grade == "B":
print("Good job!")
elif grade == "C":
print("Satisfactory.")
else:
print("Needs improvement.")
Execute code if all previous conditions were False. it's an 0ptional companion to if and elif.
if condition:
# Code to execute if condition is True
else:
# Code to execute if condition is False
Place if statements within other if blocks for complex logic.
# Example:
if has_ticket:
if ticket_type == "VIP":
print("Access to VIP lounge.")
else:
print("Access to regular seating.")
else:
print("Please purchase a ticket.")
Executes a single expression if a condition is True. Combines if and else in a single line.
value = x if condition else y
# Example
result = "even" if number % 2 == 0 else "odd"
Combine multiple conditions using and, or, and not.
Logical operators in if statements let you write concise, specific, and readable conditionals to handle diverse scenarios and optimize code.
if age >= 18 and has_license:
print("You can drive.")
another example
if a > b and a > c:
print("a is greater")
elif b > c:
print("b is greater")
else:
print("c is greater")
The in-operator in Python allows you to check if an element exists within a sequence like a list, string, or tuple. It's commonly used in if statements to make decisions based on membership.
Here are some real-time examples:
Example 1
Validating user input:
valid_chars = "abcdefghijklmnopqrstuvwxyz"
letter = input("Enter a letter: ")
if letter in valid_chars:
print(f"{letter} is a valid lowercase letter.")
else:
print("Invalid input. Please enter a lowercase letter.")
Example 2:
Checking item availability in a store:
shopping_cart = ["apples", "milk", "bread"]
item = input("What item are you looking for? ")
if item in shopping_cart:
print(f"Yes, we have {item} in stock!")
else:
print(f"Sorry, we don't have {item} in stock.")
Example 3:
Filtering data based on specific criteria:
fruits = ["apple", "banana", "orange", "grape"]
citrus_fruits = ["lemon", "lime", "grapefruit"]
if "grape" in fruits and "grape" not in citrus_fruits:
print("Grape is in the fruits list but not in the citrus fruits list.")
Example 4:
Validating passwords with specific requirements:
password = input("Enter your password: ")
required_chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
if len(password) >= 8 and any(char in required_chars for char in password):
print("Password is valid.")
else:
print("Password must be at least 8 characters long and contain at least one uppercase letter, one lowercase letter, and one digit.")
While the in operator checks if an element exists within a sequence, identity operators in Python (is and is not) compare object references themselves, not the values they hold. This distinction becomes crucial when dealing with mutable objects in if statements.
Example
Checking for the same object
x = [1, 2, 3]
y = x # Same object reference
z = [1, 2, 3] # Different object with same values
if x is y:
print("x and y are the same object") # True
else:
print("x and y are different objects")
if x is z:
print("x and z are the same object") # False
else:
print("x and z are different objects") # TrueExample 2:
a = [1, 2, 3]
b = [1, 2, 3]
if a is b:
print("a and b are the same object")
else:
print("a and b are different objects") # True
a.append(4)
if a is b:
print("a and b are still the same object") # False now!
else:
print("a and b are now different objects") # True because modifying a changed its reference
Used as a placeholder when a statement is required syntactically but no action is needed.
# Example:
if age > 13:
pass # Do nothing for kids
else:
print("Welcome!")
Here are some real-time examples of how you can use it:
Empty Blocks:
In conditional statements like if, elif, and else, sometimes you have empty blocks where you haven't decided what to do yet.
if age >= 18:
# Grant access
pass
else:
# Handle underage user
pass
Incomplete Code Stubs:
For incomplete code structure, pass holds the place while avoiding errors.
def cal_salary():
# Implementation here...
pass
Loop Control:
pass in loops: skipping iterations, keeping structure
for item in items:
if item.is_hidden:
pass # Skip hidden items
else:
# Process visible items
pass
Write a program that checks if a number is positive or negative.
num = int(input("Enter a number: "))
if num > 0:
print("The number is positive.")
else:
print("The number is zero.")
Write a program that checks if a number is positive, negative, or zero.
num = int(input("Enter a number: "))
if num > 0:
print("The number is positive.")
elif num < 0:
print("The number is negative.")
else:
print("The number is zero.")
Write a program that determines the discount applicable based on age (child, teenager, adult, senior).
age = int(input("Enter your age: "))
if age <= 12:
discount = 50 # Child discount
elif age <= 18:
discount = 25 # Teenager discount
elif age <= 65:
discount = 10 # Adult discount
else:
discount = 15 # Senior discount
print("Your discount is", discount, "%")
Write a program that tells if a person is eligible to vote based on their age (voting age is 18).
age = int(input("Enter Age: "))
r = "yes" if age >= 18 else "no"
print(r)
Print “Welcome!” if the user's age is 18 or above.
Which code best achieves this?
a) if age == 18:
b) if age <= 18: c) if age >= 18:
Check if a letter is a vowel.
Which code would you use?
a) if letter in “aeiou”
b) if letter == “vowel”
c) if letter == vowel:
You need to check if a user's password is long enough (8 characters or more).
Which code achieves this?
a) if len(password) >= 8: print(“Valid”)
b) if len(password) < 8: print(“Too short”)
c) if len(password) == 8: print(“Valid “)
You need to allow access to a website only for users above 13 and with a valid membership.
Which code correctly represents this check?
a) if age >= 13 and member:
b) if age >= 13 or member:
c) if age > 13 and member == True: