Python Exception Handling – Basic Examples

Byadmin

1. Basic try-except Block

python

# Basic exception handling
try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except:
    print("Something went wrong!")

Example 1: Division with Zero Handling

python

# Handling division by zero error
try:
    num1 = int(input("Enter first number: "))
    num2 = int(input("Enter second number: "))
    result = num1 / num2
    print(f"Result: {result}")
except ZeroDivisionError:
    print("Error: Cannot divide by zero!")

Output:

text

Enter first number: 10
Enter second number: 0
Error: Cannot divide by zero!

Example 2: Invalid Input Handling

python

# Handling invalid input (non-integer values)
try:
    age = int(input("Enter your age: "))
    print(f"Your age is: {age}")
except ValueError:
    print("Error: Please enter a valid number!")

Output:

text

Enter your age: twenty
Error: Please enter a valid number!

Example 3: File Operations

python

# Handling file not found error
try:
    with open("non_existent_file.txt", "r") as file:
        content = file.read()
        print(content)
except FileNotFoundError:
    print("Error: File not found!")

Output:

text

Error: File not found!

Example 4: List Index Error

python

# Handling index out of range error
fruits = ["apple", "banana", "cherry"]

try:
    index = int(input("Enter index (0-2): "))
    print(f"Fruit at index {index}: {fruits[index]}")
except IndexError:
    print("Error: Index out of range!")
except ValueError:
    print("Error: Please enter a valid number!")

Output:

text

Enter index (0-2): 5
Error: Index out of range!

Example 5: Dictionary Key Error

python

# Handling key not found in dictionary
student = {"name": "John", "age": 20, "grade": "A"}

try:
    key = input("Enter key to search (name/age/grade): ")
    print(f"{key}: {student[key]}")
except KeyError:
    print(f"Error: Key '{key}' not found in dictionary!")

Output:

text

Enter key to search (name/age/grade): city
Error: Key 'city' not found in dictionary!

Bonus Example: Multiple Exception Handling

python

# Handling multiple types of exceptions
try:
    num = int(input("Enter a number: "))
    result = 100 / num
    print(f"100 divided by {num} is {result}")
    
except ValueError:
    print("Error: Please enter a valid integer!")
except ZeroDivisionError:
    print("Error: Cannot divide by zero!")
except Exception as e:
    print(f"Unexpected error: {e}")

Output:

text

Enter a number: abc
Error: Please enter a valid integer!

Key Points:

  1. try block: Contains code that might raise exceptions
  2. except block: Catches and handles specific exceptions
  3. Specific exceptions: Better than catching all exceptions
  4. User-friendly messages: Help users understand what went wrong
  5. Prevention: Better than handling errors after they occur

These examples show how to gracefully handle common errors that might crash your program!

1. Basic try-except Block

python

# Basic exception handling
try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except:
    print("Something went wrong!")

2. Handling Specific Exceptions

python

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except ValueError:
    print("Please enter a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")

3. Handling Multiple Exceptions in One Block

python

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except (ValueError, ZeroDivisionError):
    print("Invalid input or division by zero!")

4. Using else Clause

python

try:
    num = int(input("Enter a number: "))
    result = 10 / num
except ValueError:
    print("Please enter a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")
else:
    print(f"Success! Result: {result}")  # Only runs if no exceptions

5. Using finally Clause

python

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except ValueError:
    print("Please enter a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")
finally:
    print("This always executes - cleanup code goes here")

6. Getting Exception Information

python

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except Exception as e:
    print(f"Error type: {type(e).__name__}")
    print(f"Error message: {e}")

7. File Handling Example

python

try:
    with open("myfile.txt", "r") as file:
        content = file.read()
        print(content)
except FileNotFoundError:
    print("File not found!")
except PermissionError:
    print("Permission denied!")
except IOError:
    print("Error reading file!")

8. List Index Handling

python

my_list = [1, 2, 3, 4, 5]

try:
    index = int(input("Enter index (0-4): "))
    print(f"Value at index {index}: {my_list[index]}")
except ValueError:
    print("Please enter a valid integer!")
except IndexError:
    print("Index out of range!")

9. Dictionary Key Handling

python

student = {"name": "John", "age": 20, "grade": "A"}

try:
    key = input("Enter key to search (name/age/grade/city): ")
    print(f"{key}: {student[key]}")
except KeyError:
    print(f"Key '{key}' not found in dictionary!")

10. Complete Example with All Clauses

python

def divide_numbers():
    try:
        num1 = int(input("Enter first number: "))
        num2 = int(input("Enter second number: "))
        result = num1 / num2
        
    except ValueError:
        print("Please enter valid integers!")
        return None
    except ZeroDivisionError:
        print("Cannot divide by zero!")
        return None
    except Exception as e:
        print(f"Unexpected error: {e}")
        return None
    else:
        print("Division successful!")
        return result
    finally:
        print("Calculation completed!")

# Run the function
result = divide_numbers()
if result is not None:
    print(f"Final result: {result}")

11. Nested Exception Handling

python

try:
    # Outer try block
    numbers = []
    
    try:
        # Inner try block
        num = int(input("How many numbers? "))
        for i in range(num):
            value = int(input(f"Enter number {i+1}: "))
            numbers.append(value)
            
    except ValueError:
        print("Invalid number entered!")
    
    # Continue with outer block
    if numbers:
        average = sum(numbers) / len(numbers)
        print(f"Average: {average}")
        
except ZeroDivisionError:
    print("No numbers were entered!")
except Exception as e:
    print(f"Unexpected error: {e}")

12. Simple Calculator with Error Handling

python

def calculator():
    try:
        num1 = float(input("Enter first number: "))
        operator = input("Enter operator (+, -, *, /): ")
        num2 = float(input("Enter second number: "))
        
        if operator == '+':
            result = num1 + num2
        elif operator == '-':
            result = num1 - num2
        elif operator == '*':
            result = num1 * num2
        elif operator == '/':
            result = num1 / num2
        else:
            print("Invalid operator!")
            return
            
        print(f"Result: {result}")
        
    except ValueError:
        print("Please enter valid numbers!")
    except ZeroDivisionError:
        print("Cannot divide by zero!")
    except Exception as e:
        print(f"An error occurred: {e}")

# Run calculator
calculator()

13. Input Validation with Retry

python

def get_valid_number():
    while True:
        try:
            num = int(input("Enter a positive number: "))
            if num <= 0:
                raise ValueError("Number must be positive!")
            return num
        except ValueError as e:
            print(f"Invalid input: {e}")
            print("Please try again!")

# Usage
number = get_valid_number()
print(f"You entered: {number}")

Key Points to Remember:

  1. try: Code that might raise exceptions
  2. except: Handles specific exceptions
  3. else: Runs if no exceptions occur
  4. finally: Always runs (good for cleanup)
  5. Use specific exceptions instead of general except:
  6. Always handle exceptions gracefully for better user experience

These examples cover the fundamental concepts of exception handling in Python!

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