print & input

Overview

print() and input() are the primary tools for console interaction. Knowing their parameters (sep, end, file, flush) and how to handle input type conversion is essential for scripts and interview exercises.

Syntax

python

# print() parameters
print("Hello", "World", sep=", ", end="!
")
# Hello, World!

print("Loading...", end="", flush=True)

# input() always returns a string
name = input("Enter your name: ")
age = int(input("Enter your age: "))  # convert to int

Common Pitfalls

input() always returns a string — forgetting to convert with int() or float() causes subtle TypeErrors in arithmetic.
Use try/except ValueError around int(input()) to handle non-numeric user input gracefully.
Interview tip: In competitive programming contexts, use sys.stdin.readline() for faster input than input().

Real-World Example

Simple interactive CLI calculator

example

python

def calculator():
    try:
        a = float(input("First number: "))
        op = input("Operator (+, -, *, /): ")
        b = float(input("Second number: "))
        
        operations = {"+": a + b, "-": a - b, "*": a * b}
        if op == "/" and b == 0:
            print("Error: division by zero")
        else:
            result = operations.get(op, "Unknown operator")
            print(f"Result: {result}")
    except ValueError:
        print("Invalid number entered")

calculator()

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