Table of contents

1. Errors
   1. Syntax Errors
   2. Exceptions Errors
   3. User Customized Errors:
   4. How to handle execptions

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Errors

Syntax Errors

• Occurs during compiling time (before program is executed)
• Example: if True print("Hello")
• Output: SyntaxError: invalid syntax

Exceptions Errors

• Occurs during program executions, all default execptions are built-in
• Different built in errors (i.e. there are 11 of them)

1. TypeError
   • Occurs when operation/function is applied to an object of a wrong type
   • Example: len(4)
   • Output: TypeError: object of type ‘int’ has no len()
2. ValueError
   • Occurs when functions inputs got the right type but wrong value
   • Example: int("abc")
   • Output: ValueError: invalid literal for int() with base 10: ‘abc’
3. IndexError
   • Occurs when index is out of range
   • Example:

     lst = [1, 2, 3]
     print(lst[5])
     

   • Output: IndexError: list index out of range
4. KeyError
   • Occurs when dict key is not found
   • Example:

     d = {"a": 1}
     print(d["b"])
     

   • Output: KeyError: ‘b’
5. AttributeError
   • Occurs when method/attribute is not found
   • Example:

     obj = None
     obj.method()
     

   • Output: AttributeError: ‘NoneType’ object has no attribute ‘method’
6. NameError
   • Occurs when local/global var of the object is not found
   • Example:

     print(x)
     

   • Output: NameError: name ‘x’ is not defined
7. ZeroDivisionError
   • Occurs when you divide by 0
   • Example:

     1 / 0 
     

   • Output: ZeroDivisionError: division by zero
8. FileNotFoundError
   • Occurs when the input file/dir doesn’t exist
   • Example:

     open("non_existent_file.txt")
     

   • Output: FileNotFoundError: [Errno 2] No such file or directory: ‘non_existent_file.txt’
9. ImportError
   • Occurs when the module doesn’t exist
   • Example:

     import non_existent_package.non_existent_module as nem
     

   • Output: ImportError: No module named ‘non_existent_module’
10. IndentationError
    • Occurs during incorrect identation
    • Example:

      def func():
      print("Hello")
      

    • Output: IndentationError: expected an indented block
11. RuntimeError
    • Occurs when error doesn’t belong in any of the 10 exceptions + 1 Syntax Error
    • Example:

      raise RuntimeError("This is a runtime error")  
      

    • Output: RuntimeError: This is a runtime error

User Customized Errors:

• class MyCustomErrors(Exception):
      pass
  
  raise MyCustomErrors("This is a custom error")
  

How to handle execptions

• Example 1

    try:
        # Code that may raise an exception
        result = 1 / 0
  
    # Could be executed
    except ZeroDivisionError as e:
        # Handle the exception
        print(f"Caught an exception: {e}")
    # Could be executed
    else: 
        # Code to execute if no exception occurs !
        print("No exception occurred")
    finally: # Code will ALWAYS execute!!
        # Code to execute regardless of whether an exception occurs or not
        print("This will always execute")
  
  

• Example 2:

    try:
        num = int(input("Enter a number: "))
        result = 10 / num
    except ValueError:
        print("❌ Invalid input. Please enter a valid integer.")
    except ZeroDivisionError:
        print("❌ Cannot divide by zero.")
    else:
        print(f"✅ Result is {result}")
    finally:
        print("🔹 Program finished.")
  
    '''
    How it works:
  
    If the user enters a non-integer → ValueError is caught.
    If the user enters 0 → ZeroDivisionError is caught.
    If no error → else block runs.
    finally always runs
    '''
  

High level idea:

• ending 1: try -> except -> finally
• ending 2: try -> else -> finally