Concept Notes (Deep Explanation + Examples)
🔹 Introduction
In Python programming, Exception Handling is one of the most important topics—both for ECET and real-world coding.
Whenever a program crashes, it’s usually due to an error or exception.
To make your program error-proof and user-friendly, Python gives special tools:try, except, else, finally, and raise.
🔹 What is an Exception?
An Exception is an unexpected event that occurs during the execution of a program, disrupting the normal flow.
🧠 Example:
x = int(input("Enter a number: "))
y = int(input("Enter another number: "))
print("Division result:", x / y)If you input y = 0, the program stops with:
ZeroDivisionError: division by zeroThat’s an exception!
🔹 Why Exception Handling?
✅ Prevents program crashes
✅ Displays user-friendly error messages
✅ Helps debug complex systems
✅ Ensures important code always runs (like saving data or closing files)
🔹 Python Exception Handling Keywords
| Keyword | Use |
|---|---|
try | Block where you test code for errors |
except | Handles the error if found |
else | Executes if no error occurs |
finally | Executes always (used for cleanup) |
raise | Manually trigger an exception |
🔹 Basic Example
try:
a = int(input("Enter number: "))
b = int(input("Enter another: "))
print(a / b)
except ZeroDivisionError:
print("Cannot divide by zero!")
except ValueError:
print("Please enter valid numbers!")
else:
print("Division successful!")
finally:
print("Program Ended.")🧩 Output (Case 1)
If a = 10, b = 0 → Output:
Cannot divide by zero!
Program Ended.🧩 Output (Case 2)
If a = 10, b = 2 → Output:
5.0
Division successful!
Program Ended.🔹 Real-World Example
Imagine a student marks management system in ECET practice software:
try:
marks = int(input("Enter marks: "))
if marks < 0:
raise ValueError("Marks cannot be negative!")
print("Marks recorded:", marks)
except ValueError as e:
print("Error:", e)📘 Explanation:
If the user enters -10, it raises a custom message.
This ensures your system doesn’t store invalid values — a real-world safeguard.
🔹 Nested Try Blocks
You can also nest try blocks for more detailed control.
try:
try:
num = int(input("Enter number: "))
print(10 / num)
except ZeroDivisionError:
print("Inner Block: Division by Zero")
except ValueError:
print("Outer Block: Invalid Number")🔹 Diagram (Explained in Words)
🧭 Imagine a flowchart:
1️⃣ Program enters try block
2️⃣ If error → jumps to matching except block
3️⃣ If no error → executes else
4️⃣ Finally → executes always
This logical flow ensures no runtime crash.
🔹 ECET Important Points
💡 1. Exception handling improves program reliability
💡 2. Multiple excepts can handle different error types
💡 3. The finally block executes always
💡 4. raise helps in custom error creation
💡 5. Frequently asked ECET question: difference between error and exception
3️⃣ ⚙️ Formulas (Plain LaTeX, No Boxes)
4️⃣ 🔟 10 MCQs (ECET + GATE Hybrid)
1. Which block in Python is always executed, even if an exception occurs?
A) try
B) except
C) finally
D) raise
2. What happens if no exception occurs in the try block?
A) except block executes
B) else block executes
C) finally block skipped
D) program crashes
3. What does the raise keyword do?
A) Stops execution
B) Handles exceptions
C) Generates an exception manually
D) Resumes program
4. Which of the following is a built-in Python exception?
A) DivideError
B) NullError
C) ValueError
D) InputException
5. What is the output of the code?
try:
print(1/0)
except:
print("Error")
finally:
print("Done")A) Error
B) Error Done
C) Done Error
D) None
6. Which keyword is used to handle exceptions in Python?
A) catch
B) handle
C) except
D) error
7. Which block is used to test the code for errors?
A) except
B) finally
C) try
D) raise
8. Which statement correctly handles multiple exceptions?
A) except (ValueError, TypeError):
B) except ValueError, TypeError:
C) catch (ValueError, TypeError):
D) try (ValueError, TypeError):
9. What is the output of:
try:
x = 5/2
except ZeroDivisionError:
print("Error")
else:
print("No Error")A) Error
B) No Error
C) 2.5
D) Both B and C
10. What is printed?
try:
a = 10
b = "5"
c = a + b
except TypeError:
print("Type Error")A) No Error
B) Type Error
C) Value Error
D) Syntax Error
5️⃣ ✅ Answer Key (WordPress Table — NO HTML)
Q No | Answer
1 | C
2 | B
3 | C
4 | C
5 | B
6 | C
7 | C
8 | A
9 | D
10 | B
6️⃣ 🧠 MCQ Explanations
1️⃣ C – finally
The finally block executes regardless of exceptions — used for cleanup.
2️⃣ B – else block executes
If no exception occurs, the else block runs.
3️⃣ C – Generates exception manuallyraise is used to manually throw exceptions.
4️⃣ C – ValueError
It’s a predefined exception type.
5️⃣ B – Error Done
First except prints “Error”, then finally prints “Done”.
6️⃣ C – except
Used to handle errors after try.
7️⃣ C – try
Used to test code for exceptions.
8️⃣ A – except (ValueError, TypeError):
Correct syntax for multiple exceptions.
9️⃣ D – Both B and C
Output prints No Error and result 2.5.
10️⃣ B – Type Error
Adding int + string raises a TypeError.
7️⃣ 🎯 Motivation (ECET 2026 Specific)
🔥 Why this topic repeats every year:
Exception Handling is a favorite among ECET and GATE setters because it tests your concept clarity and code reliability.
Even a small syntax question can decide your rank jump.
💡 Tip:
In your ECET coding section, always write safe programs using try-except.
This one skill can make your code look professional and error-free.
8️⃣ 📲 CTA (Fixed)
Join our ECET 2026 CSE WhatsApp Group for daily quizzes & study notes:
👉 https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9
