Python Exception Handling

Exception Handling in Python

• Python has built-in exceptions that are raised when something goes wrong.
• Exceptions can be handled using a try statement.
• Code that handles the exception is written in the except clause.
• After an exception is handled, the code flow continues without program interruption.
• Example try-except structure:
  • try: # Code
  • except Exception as e: print(e) where the arrow indicates code which might throw an exception, and the type of exception thrown.
• Specific exceptions can be caught:
  • try: # Code
  • except ZeroDivisionError: # Code
  • except TypeError: # code
  • except: # Code (Handles all other exceptions)
• Custom exceptions can be raised using the raise keyword in Python.

Try with Else Clause

• The else clause in a try block runs a piece of code when the try block is successful.
• Example structure:
  • try: # Some code
  • except: # Some Code
  • else: # Code (This is executed only if the try was successful)

Try with Finally

• Python offers a finally clause which ensures execution of a piece of code irrespective of the exception.
• Example structure:
  • try: # Some code
  • except: # Some code
  • finally: # Some Code (executed regardless of error!)

__name__ == '__main__' in Python

• __name__ evaluates to the name of the module in Python from where the program is run.
• If the module is run directly from the command line, __name__ is set to the string __main__.
• This behavior is used to check whether the module is run directly or imported to another file.

Global Keyword

• The global keyword is used to modify the variable outside of the current scope.

Enumerate Function in Python

• The enumerate function adds a counter to an iterable and returns it.
• Example usage:
  • for i, item in list1: print(i, item) (Prints the items of list 1 with index!)

List Comprehensions

• List comprehension is an elegant way to create lists based on existing lists.
• Example
  • list1 = [1, 7, 12, 11, 22]
  • list2 = [i for item in list1 if item > 8]