Mastering Python Conditional Statements: if, if-else, if-elif-else & More
Python’s conditional statements help in decision-making by executing code blocks based on specified conditions. Understanding if
, if-else
, and if-elif-else
statements is crucial for writing logical and efficient programs. Let’s explore them with practical examples.
1. The if
Statement
The if
statement evaluates a condition, and if it holds True
, the corresponding block of code executes.
if True: print("Statement is true") if False: print("Statement is false") # This will not execute
Example:
x = 20 if x > 10: print("X is greater than 10") x = 20 if x < 10: print("X is less than 10") # No output, as the condition is False
Checking Membership in Lists:
L = [10, 20, 30, 40, 50] if 20 in L: print("20 is a member of L")
2. The if-else
Statement
The if-else
structure helps define an alternative action if the condition is False.
x = 20 if x > 10: print("X is greater than 10") else: print("X is less than 10")
Example: Checking Even or Odd Numbers
values = {} x = int(input("Enter a value: ")) if x % 2 == 0: values[str(x)] = "Even" else: values[str(x)] = "Odd" print(values)
3. The if-elif-else
Statement
When multiple conditions need evaluation, the if-elif-else
structure is useful.
mark = 75 if mark >= 80: Grade = "A" elif mark >= 65: Grade = "B" elif mark >= 50: Grade = "C" else: Grade = "Repeat" print(Grade)
Using Logical Operators in Conditions
Python supports logical operators (and
, or
, not
) to create complex conditions.
Example: Using and
x = 30 if x > 10 and x < 50: print("X is in the correct region") else: print("X is out of the region")
Example: Using or
x = 30 if x > 10 or x == 50: print("X is in the correct region") else: print("X is out of the region")
Example: Using not
x = 30 if not x > 10 or x == 50: print("X is in the correct region") else: print("X is out of the region")
5. Implementing Login Authentication with if-else
details = {"Sam": "ABC", "Kane": "XYZ", "Jane": "PQR"} username = input("Please enter your username: ") if username in details: password = input("Please enter your password: ") if password == details[username]: print("You have logged in successfully!!!") else: print("Check your password...") else: print("You are not in the system. Please check your username again.")
6. Inline Decision Making (Ternary Operator)
Python provides a concise way to write simple if-else
conditions in a single line.
Example:
x = 20 y = 10 if x > 10: y = 30 print(y) # Output: 30
Using a Ternary Operator:
fruit = 'Apple' check_apple = "Yes" if fruit == 'Apple' else "No" print(check_apple) # Output: Yes
Assigning Grades Conditionally:
mark = 90 grade = "A" if mark >= 80 else "B" if mark >= 65 else "C" if mark >= 50 else "F" print(grade) # Output: A