In Python, understanding expressions, statements, and input/output (I/O) is essential for writing interactive and functional programs.
1. Expressions in Python
An expression is a combination of values, variables, operators, and function calls that evaluate to a single value.
Examples:
x = 10 + 5 # Expression: 10 + 5
area = 3.14 * (5 ** 2) # Expression with multiplication and exponentiation
result = (10 > 5) and (5 < 8) # Expression with logical operators
Expressions can be used inside print statements, assignments, and conditions.
print(2 * 3 + 5) # Output: 11
Types of Expressions:
- Arithmetic Expressions:
x + y * z - Relational Expressions:
a > b - Logical Expressions:
x and y - String Expressions:
'Hello' + ' World' - Function Call Expressions:
len('Python')
2. Statements in Python
A statement is an instruction that Python can execute. Unlike expressions, statements do not return a value.
Types of Statements:
- Assignment Statement:
x = 10 # Assigns 10 to x
- Conditional Statement:
if x > 5:
print("x is greater than 5")
- Loop Statement:
for i in range(5):
print(i)
- Function Definition Statement:
def greet():
print("Hello, Python!")
- Import Statement:
import math
print(math.sqrt(16)) # Output: 4.0
Statements are executed sequentially unless control flow mechanisms like loops or conditionals change the execution order.
3. Input in Python
The input() function allows users to enter data into a program.
Example:
name = input("Enter your name: ")
print("Hello, " + name + "!")
By default, input() returns a string. To accept numerical input, type conversion is needed:
age = int(input("Enter your age: "))
print("Next year, you will be", age + 1)
4. Output in Python
The print() function is used to display output on the screen.
Basic Example:
print("Hello, World!")
Using Variables in print():
name = "Alice"
age = 25
print("Name:", name, "Age:", age)
Formatted Output with f-strings:
name = "Bob"
age = 30
print(f"My name is {name} and I am {age} years old.")
Printing with sep and end Parameters:
print("Hello", "Python", sep="-", end="!")
# Output: Hello-Python!
5. Summary
✅ Expressions evaluate to a value and can be used in operations.
✅ Statements are executed sequentially and include assignments, loops, and conditionals.
✅ Input in Python is handled using input().
✅ Output is displayed using print(), with advanced formatting options.