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Learning outcomes

By the end of this chapter, you should be able to:
  • use input() for user input
  • convert input into required data type
  • take multiple values in one line
  • print clean output using formatting

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30-minute recording plan

  • 0-6 min: input() fundamentals
  • 6-13 min: type conversion (int, float)
  • 13-20 min: multiple inputs with split() and map()
  • 20-26 min: formatted output using f-strings
  • 26-30 min: common input mistakes and MCQ recap

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Input workflow (important)

Most beginner input bugs happen because steps are skipped.
  1. read value with input()
  2. convert to required type (int, float, etc.)
  3. process using formula/logic
  4. print final result clearly

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Basic input

name = input("Enter your name: ")
print("Hello", name)
Important: input() always returns a string.

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Numeric input with conversion

age = int(input("Enter age: "))
height = float(input("Enter height in meters: "))
Use:
  • int() for integers
  • float() for decimals
If you skip conversion, numeric operations may fail or give wrong output.

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Multiple inputs in one line

a, b = input("Enter two numbers: ").split()
a = int(a)
b = int(b)
print(a + b)
Enter values separated by a space, for example: 10 20. This version expects whole numbers; if you enter decimals like 12.5, int() will raise ValueError. Short form: 
a, b = map(int, input("Enter two numbers: ").split())
print(a + b)

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Sequence unpacking from a single string (MCQ-critical)

Python can unpack characters of a string directly: 
a, b = "56"
print(a, b)  # 5 6
This works because string "56" has exactly 2 characters. Same pattern with user input: 
a, b = input("Enter exactly 2 characters: ")
Rules:
  • number of variables must match number of characters
  • otherwise ValueError occurs
Examples: 
# a, b = "5"      # ValueError (not enough values)
# a, b = "567"    # ValueError (too many values)
Important difference:
  • a, b = input().split() splits by spaces into words/tokens
  • a, b = input() unpacks raw characters directly

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Digit extraction trap from input (sandwich-number type)

Question style:
  • “Take a 3-digit number.”
  • “Compare first + last with middle digit.”
Common wrong implementation: 
num = int(input())
first, middle, last = num[0], num[1], num[2]  # wrong
Why wrong:
  • int values are not subscriptable.
  • indexing like num[0] works for strings/lists, not ints.
Another wrong pattern: 
num = input()
first, middle, last = num[0], num[1], num[2]
if first + last == middle:
    print("sandwich")
Why wrong:
  • first, middle, last are strings.
  • first + last concatenates (for 143, "1" + "3" -> "13"), not numeric sum.
Correct pattern: 
num = input().strip()        # e.g., "143"
first, middle, last = map(int, num)

if first + last == middle:
    print("sandwich")
else:
    print("plain")

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Beginner alert: what map() means

This one-liner is common in exams, but it hides 3 steps:
  1. input(...).split() gives a list of strings
  2. map(int, ...) converts each string to integer
  3. a, b = ... unpacks the two integers into two variables
Same logic in expanded form: 
parts = input("Enter two numbers: ").split()  # ['10', '20']
a = int(parts[0])
b = int(parts[1])
print(a + b)
When can the one-liner fail?
  • If user enters fewer or more than 2 values: unpacking error
  • If user enters non-numeric text (like ten): ValueError
  • If user enters decimals while using int (like 12.5): ValueError (use float instead)

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Output formatting

name = "Dhruv"
marks = 87
print(f"{name} scored {marks} marks")
f"..." formatting is clean and exam-safe. The f means “formatted string”, so variables inside {} are replaced by values.

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Mini showcase: simple marks report

name = input("Name: ")
m1, m2, m3 = map(int, input("Enter 3 marks: ").split())

total = m1 + m2 + m3
avg = total / 3

print(f"Student: {name}")
print(f"Total: {total}")
print(f"Average: {avg:.2f}")
{avg:.2f} means: show avg with exactly 2 digits after decimal. Sample run:
  • Input: Aarav and 78 84 91
  • Output shows total and average with 2 decimal places.

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Common mistakes

  • forgetting type conversion after input()
  • using + between string and integer
  • expecting input() to return int automatically

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Exam-focused points

  • default return type of input() is str
  • type conversion functions: int(), float(), str()
  • split() returns a list of strings
  • unpacking can be done from token list (split) or directly from string characters

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Practice questions

  1. Take length and breadth as input and print area.
  2. Take 3 marks and print total and average.
  3. Write program to input name, class, and roll number and print in one formatted line.
  4. Predict output:
a, b = "89"
print(int(a) + int(b))