Python Error Handling

Python Error Handling

Python error handling involves managing exceptions that occur during program execution. Proper error handling ensures your program runs smoothly and fails gracefully when unexpected conditions occur.

Key Concepts in Python Error Handling

• Exceptions: Runtime issues that interrupt the usual execution of a program:

  • ZeroDivisionError
  • FileNotFoundError
  • ValueError
  • TypeError

• try and except:

  • The try block encloses code that could trigger an exception.
  • The except block intercepts and processes exceptions.

• else: Executes code if no exceptions occur in the try block.

• finally: Executes code regardless of whether an exception was raised or not.

• Raising Exceptions: You can explicitly raise exceptions using the raise statement.

• Custom Exceptions: You can define your own exceptions by creating a class derived from the Exception class.

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Syntax and Examples

1. Basic try and except

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  try:
      num = int(input("Enter a number: "))
      result = 10 / num
      print(f"Result: {result}")
  except ZeroDivisionError:
      print("Error: You cannot divide by zero.")
  except ValueError:
      print("Error: Invalid input. Please enter a number.")
 

2. Using else

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  try:
      num = int(input("Enter a number: "))
      result = 10 / num
  except ZeroDivisionError:
      print("Error: You cannot divide by zero.")
  else:
      print(f"Result: {result}")
 

3. Using finally

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  try:
      file = open("example.txt", "r")
      content = file.read()
      print(content)
  except FileNotFoundError:
      print("Error: File not found.")
  finally:
      print("Execution completed, cleaning up...")
 

4. Raising Exceptions

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  def check_positive(number):
  if number < 0:
          raise ValueError("The number must be positive.")
      return number

  try:
      print(check_positive(-5))
  except ValueError as e:
      print(f"Error: {e}")

5. Creating Custom Exceptions

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  class CustomError(Exception):
      pass

  def check_condition(value):
      if value != "expected":
          raise CustomError("Unexpected value provided!")

  try:
      check_condition("unexpected")
  except CustomError as e:
      print(f"Caught a custom exception: {e}")
 

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Explanation of Each Block

• try: Protects the code that might cause an exception.
• except: Specifies how to handle specific exceptions.
• else: Block runs only when the try block executes without errors.
• finally: Ensures that clean-up code runs, like closing files or releasing resources.

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Best Practices

• Be specific in exception handling to avoid masking unintended errors.

    except (ValueError, TypeError):  # Catch specific exceptions
  

• Avoid a generic except: as it captures all exceptions, including SystemExit and KeyboardInterrupt.
• Always clean up resources using finally or context managers.
  Copy code

    with open("example.txt", "r") as file:
      content = file.read()
  

By mastering error handling, you can make your Python programs more robust and user-friendly!