Exception Handling

1. What is Exception Handling

Exception handling is the mechanism used to detect, manage, and respond to runtime errors without crashing the program.

x = 10
y = 0

print(x / y)  # Raises ZeroDivisionError

Without handling, the program terminates abruptly.

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2. Basic try-except Block

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero")

Safely captures and handles runtime exceptions.

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3. Handling Multiple Exceptions

try:
    value = int("abc")
except (ValueError, TypeError):
    print("Conversion failed")

Handles multiple exception types in a single block.

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4. Generic Exception Handling

try:
    risky_operation()
except Exception as e:
    print("Error:", e)

Catches any unexpected runtime error.

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5. Using else with try-except

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Error occurred")
else:
    print("Success:", result)

else executes only when no exception occurs.

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6. Using finally Block

try:
    file = open("data.txt")
except FileNotFoundError:
    print("File not found")
finally:
    print("Cleanup complete")

Ensures cleanup execution regardless of outcome.

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7. Raising Exceptions Manually

def withdraw(balance, amount):
    if amount > balance:
        raise ValueError("Insufficient balance")
    return balance - amount

Used for enforcing business rules.

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8. Custom Exception Handling Pattern

class InvalidAgeError(Exception):
    pass

def validate_age(age):
    if age < 18:
        raise InvalidAgeError("Age must be at least 18")

Enables domain-specific error design.

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9. Chained Exceptions

try:
    int("xyz")
except ValueError as e:
    raise RuntimeError("Parsing failed") from e

Preserves original error trace.

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10. Enterprise-Grade Exception Handling Example

def process_order(order):
    try:
        if "id" not in order:
            raise KeyError("Missing Order ID")

        amount = order["amount"]
        if amount <= 0:
            raise ValueError("Invalid order amount")

        return "Order processed successfully"

    except (KeyError, ValueError) as e:
        return f"Order error: {e}"

print(process_order({"amount": -50}))

Common in microservices, validation systems, and API pipelines.

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Exception Handling Flow

Block	Purpose
try	Code that may fail
except	Handle error
else	Executes if no error
finally	Always executes

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Common Exception Types

Exception	Scenario
ZeroDivisionError	Division by zero
ValueError	Wrong data type or value
TypeError	Wrong argument type
FileNotFoundError	Missing file
KeyError	Missing dictionary key

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Best Practices

• Avoid bare except clauses

• Catch specific exceptions

• Log exceptions for diagnostics

• Use custom exceptions for domain logic

• Avoid suppressing critical errors

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Common Mistakes

• Overusing generic except Exception

• Silent exception swallowing

• Mixing logic and error handling

• Not re-raising critical exceptions

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Enterprise Importance

Proper exception handling ensures:

• Application stability

• Fault tolerance

• Graceful degradation

• Traceable error diagnostics

• System resiliency

Crucial in:

• Distributed systems

• Financial applications

• AI model inference engines

• DevOps pipelines

• API error management

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