Input and Output

Topic — Reading data from the user with input(), and controlling what print() puts on screen.

---

input() — reading from the user

input() accepts data from the user during program execution (at runtime). It pauses the program, waits for a line to be typed, and hands it back as a value.

age = input("Enter age: ")
print(type(age))

Output (typing 25)

Enter age: 25
<class 'str'>

The string passed to input() is the prompt — the message displayed before the cursor. It's optional:

city = input()             # no prompt — just waits
print("I am from", city)

Output (typing Chennai)

Chennai
I am from Chennai

With a prompt, it's clearer what's expected:

city = input("Enter Your City: ")
print("I am from", city)

Output

Enter Your City: Chennai
I am from Chennai

input() ALWAYS returns a string

This is the single most important thing on this page. Even when the user types digits, you get a str:

age = input("Enter age: ")   # user types 25
print(type(age))             # → <class 'str'>
# age + 5  →  TypeError: can only concatenate str (not "int") to str

Wrap it in int() (or float()) to do arithmetic:

age = int(input("Enter age: "))
print(type(age))     # → <class 'int'>
print(age + 5)       # → 30

Output

Enter age: 25
<class 'int'>
30

warning

int(input()) raises ValueError if the user types something that isn't a whole number:

try:
    age = int(input("Enter age: "))
except ValueError as error:
    print("ValueError:", error)

Output (typing abc)

Enter age: ValueError: invalid literal for int() with base 10: 'abc'

Also note int("25.5") fails too — go through float first. See Values and Types.

What you want	Write
Text	name = input("Name: ")
Whole number	age = int(input("Age: "))
Decimal	price = float(input("Price: "))
Yes/no flag	flag = input("Continue? ").lower() == "y"

---

print() — writing to the screen

print() takes any number of values, plus two parameters that control how they're joined and how the line ends:

print(value1, value2, ..., sep=' ', end='\n')

Multiple values

Pass as many as you like, separated by commas. print() converts each to text for you — no str() needed:

name = "Rahul"
age = 20
print(name, age)

Output

Rahul 20

Note the space between them. That's sep doing its default job.

Parameter sep — what goes between values

Default is a single space.

print("Python", "Java", "C")
print("Python", "Java", "C", sep=", ")
print("Python", "Java", "C", sep=" | ")
print("A", "B", sep="")

Output

Python Java C
Python, Java, C
Python | Java | C
AB

Parameter end — what goes after the last value

Default is "\n", a newline — which is why every print() normally starts a fresh line.

print("Hello")
print("World")

Output

Hello
World

Change end and the next print() continues on the same line:

print("Hello", end=" ")
print("World")

Output

Hello World

print("Python", end="---")
print("Programming")

Output

Python---Programming

tip

end=" " is how you print a loop's results on one line:

for i in range(1, 6):
    print(i, end=" ")
print()          # a bare print() ends the line

Output

1 2 3 4 5

The final bare print() matters — without it, the next output would run on from 5.

sep and end combine freely:

print(1, 2, 3, sep="-", end="!\n")

Output

1-2-3!

---

Printing expressions

print() prints the result, not the expression. The maths happens first:

a = 10
b = 20
print(a + b)          # → 30
print("Sum:", a + b)  # → Sum: 30

---

Printing different data types together

Unlike string concatenation with +, comma-separated print() arguments don't need converting:

student = "Rahul"
marks = 90
print("Student:", student, "Marks:", marks)

Output

Student: Rahul Marks: 90

Compare the three ways to write that same line:

print("Student:", student, "Marks:", marks)              # commas — no str() needed
print("Student: " + student + " Marks: " + str(marks))   # + — str() required on marks
print(f"Student: {student} Marks: {marks}")              # f-string — clearest

All three print the same thing. The f-string is what you'd actually write — see F-Strings.

One value per line is often the readable choice:

print("Name:", "John")
print("Age:", 30)

Output

Name: John
Age: 30

---

Common Mistakes

#	Mistake	Wrong	Right
1	Doing maths on input()	age = input(); age + 5 → TypeError	age = int(input()); age + 5
2	int() on a decimal string	int(input()) with 25.5 → ValueError	float(input()), or int(float(...))
3	Concatenating a number with +	"Age: " + 30 → TypeError	"Age:", 30 or f"Age: {30}"
4	Expecting sep between print() calls	sep only applies within one call	use end to join separate calls
5	Forgetting the bare print() after an end=" " loop	next output runs on from the last value	add print() to close the line
6	Assuming input() strips nothing	trailing spaces are kept	input().strip()

---

Summary

Function	Purpose	Key point
input(prompt)	Read one line from the user	Always returns str
int(input())	Read a whole number	ValueError on bad input
float(input())	Read a decimal	Handles 25.5
print(*values)	Write to screen	Converts each value automatically
print(..., sep=)	Text between values	Default ' '
print(..., end=)	Text after the last value	Default '\n'

Key takeaways

• input() returns a str every single time — convert before doing arithmetic
• The prompt is just the first argument to input(); it's optional
• sep controls what goes between values, end what goes after the line
• sep and end apply to a single print() call, not across calls
• print("a", 30) needs no str(); "a" + 30 does
• end=" " plus a closing bare print() is the loop-on-one-line pattern

See also: F-Strings for formatting the values you print · Values and Types for why the conversion is needed

---

Run It Yourself

This version uses fixed values instead of input() so it runs unattended:

input_output.py

# --- print() parameters ---
print("default sep:", "Python", "Java", "C")
print("comma sep:  ", end="")
print("Python", "Java", "C", sep=", ")
print("no newline: ", end="")
print("Hello", end=" ")
print("World")

# --- looping on one line ---
print("loop:       ", end="")
for i in range(1, 6):
    print(i, end=" ")
print()

# --- input() would give you a str; simulate it ---
simulated_input = "25"
print("type:       ", type(simulated_input).__name__)
print("converted:  ", int(simulated_input) + 5)

Output

default sep: Python Java C
comma sep:  Python, Java, C
no newline: Hello World
loop:       1 2 3 4 5 
type:        str
converted:   30

---

Practice Questions

From the Unit 1 question bank. Tags and marks are explained on the Python index.

Unit 1 § C — Input & Output

C1. [OUT] Assume the user types 25 at both prompts. [3]

a = input("Enter a number: ")
print(type(a))
print(a + a)

b = int(input("Enter a number: "))
print(type(b))
print(b + b)

C2. [THEORY] input() always returns one specific type, no matter what the user types. Which type, and what must you do if you need to do arithmetic on it? [2]

C3. [OUT] [4]

print("Python", "Java", "C")
print("Python", "Java", "C", sep=", ")
print("Python", "Java", "C", sep="")
print("Hello", end=" ")
print("World")
print("A", end="---")
print("B")

C4. [PROG] Accept a name, age, and city from the user. Display them exactly in this layout: [5]

Student Details
---------------
Name : Vettri
Age  : 28
City : Chennai

C5. [OUT] [3]

print("A\tB\tC")
print("Line1\nLine2")
print("She said \"Hi\"")
print('It\'s fine')
print("C:\\Users\\new")