Built-in Exceptions

Built-in exceptions are the errors that the Python interpreter already knows about. When you write code, certain mistakes happen so often that the language designers have pre-defined a specific exception for each one. These are called built-in exceptions, and they form part of Python’s standard library.

The purpose of having these ready-made exceptions is to provide a standardised solution for common errors. When a built-in exception occurs, the interpreter automatically runs the appropriate handler code. This handler displays two things: the name of the exception that was raised, and a reason explaining what went wrong. The programmer’s job is then to read that message and take the correct action to fix the problem.

The textbook lists twelve commonly occurring built-in exceptions. Here they are, in the order the book presents them:

1. SyntaxError – Raised when there is an error in the syntax of the Python code. This is the most basic mistake: you typed something the interpreter cannot parse at all.
2. ValueError – Raised when a built-in method or operation receives an argument that has the right data type but an inappropriate or mismatched value. For example, passing a string like "abc" to int() gives a ValueError because the type is correct (a string) but the value cannot be converted to an integer.
3. IOError – Raised when a file specified in a program statement cannot be opened. This could happen if the file does not exist, the path is wrong, or you lack permission.
4. KeyboardInterrupt – Raised when the user accidentally hits the Delete or Esc key while a program is running. This interrupts the normal flow of execution.
5. ImportError – Raised when the requested module definition is not found. For instance, if you try to import a module that is not installed or does not exist.
6. EOFError – Raised when the input() function reaches the end of a file condition without reading any data. This typically happens when there is no more input to read.
7. ZeroDivisionError – Raised when the denominator in a division operation is zero. Division by zero is mathematically undefined, so Python raises this exception.
8. IndexError – Raised when an index or subscript in a sequence (like a list or string) is out of range. For example, accessing my_list[10] when the list has only five elements.
9. NameError – Raised when a local or global variable name is not defined. This happens when you try to use a variable that has not been assigned a value yet.
10. IndentationError – Raised due to incorrect indentation in the program code. Python relies on consistent indentation to define blocks, and any mismatch triggers this error.
11. TypeError – Raised when an operator is supplied with a value of an incorrect data type. For example, trying to add a string and an integer with + gives a TypeError. …