Exception Handling¶

Python allows programs to catch and handle exceptions using try and except.

This allows a program to recover from errors instead of crashing.

flowchart TD
    A[try block]
    A --> B{exception occurs?}
    B -->|yes| C[except block]
    B -->|no| D[continue normally]
````

---

## 1. Basic try / except

```python
try:
    x = int("hello")
except ValueError:
    print("Conversion failed")

Output:

Conversion failed

The program continues running instead of stopping.

2. Handling Multiple Exceptions¶

try:
    x = int(input("Number: "))
    print(10 / x)
except ValueError:
    print("Invalid number")
except ZeroDivisionError:
    print("Cannot divide by zero")

Each exception type can be handled separately.

3. Catching Multiple Types Together¶

except (ValueError, TypeError):
    print("Invalid input")

This handles multiple error types with a single handler.

4. The finally Clause¶

The finally block runs regardless of whether an exception occurred.

try:
    f = open("data.txt")
finally:
    print("Done")

This is often used for cleanup tasks.

flowchart TD
    A[try]
    A --> B{exception?}
    B -->|yes| C[except]
    B -->|no| D[skip except]
    C --> E[finally]
    D --> E

5. else Clause¶

else runs only when no exception occurs.

try:
    x = int("10")
except ValueError:
    print("Bad input")
else:
    print("Success")

6. Worked Example¶

try:
    value = int(input("Enter number: "))
    result = 10 / value
    print(result)
except ValueError:
    print("Please enter a valid number")
except ZeroDivisionError:
    print("Division by zero")
finally:
    print("Program finished")

7. Good Practices¶

• catch only exceptions you expect
• keep try blocks small
• avoid using except: without specifying types

8. Summary¶

Key ideas:

• try protects code that might fail
• except handles specific exceptions
• finally always executes
• else runs when no error occurs

Exception handling allows programs to recover gracefully from unexpected situations.