Python Builtin Exceptions (original) (raw)

In Python, exceptions are events that can alter the flow of control in a program. These errors can arise during program execution and need to be handled appropriately. Python provides a set of built-in exceptions, each meant to signal a particular type of error.

We can catch exceptions using try and except blocks, allowing your program to continue running even if an error occurs. These built-in exceptions can be viewed using the **local() built-in functions as follows :

locals()['builtins']

This returns a dictionary of built-in exceptions, functions and attributes.

Python Built-in Exceptions

Here’s a table listing all the major Python built-in exceptions along with a brief :

Let’s understand each exception in detail:

1. BaseException

The base class for all built-in exceptions. **Example:

Python `

try: raise BaseException("This is a BaseException") except BaseException as e: print(e)

`

Output

This is a BaseException

**Explanation: This code manually raises a BaseException and catches it, printing the exception message.

2. Exception

The base class for all non-exit exceptions. **Example:

Python `

try: raise Exception("This is a generic exception") except Exception as e: print(e)

`

Output

This is a generic exception

**Explanation: This raises a generic Exception and handles it, printing the message.

3. ArithmeticError

Base class for all errors related to arithmetic operations. **Example:

Python `

try: raise ArithmeticError("Arithmetic error occurred") except ArithmeticError as e: print(e)

`

Output

Arithmetic error occurred

**Explanation: This raises an ArithmeticError and catches it, displaying the error message.

4. ZeroDivisionError

Raised when a division or modulo operation is performed with zero as the divisor. **Example:

Python `

try: result = 10 / 0 except ZeroDivisionError as e: print(e)

`

**Explanation: This code attempts to divide by zero, causing a ZeroDivisionError.

5. OverflowError

Raised when a numerical operation exceeds the maximum limit of a data type. **Example:

Python `

import math

try: result = math.exp(1000) # Exponential function with a large argument except OverflowError as e: print(e)

`

**Explanation: The exponential function with a large argument causes an OverflowError.

6. FloatingPointError

Raised when a floating-point operation fails. **Example:

Python `

import sys import math

sys.float_info.max = 1.79e+308 # Maximum float value

try: math.sqrt(-1.0) # This doesn't raise a FloatingPointError by default except FloatingPointError as e: print(e)

`

**Explanation: Floating-point errors are rare in Python; this code demonstrates the typical use case.

7. AssertionError

Raised when an assert statement fails. **Example:

Python `

try: assert 1 == 2, "Assertion failed" except AssertionError as e: print(e)

`

**Explanation: This code fails an assertion, raising an AssertionError.

8. AttributeError

Raised when an attribute reference or assignment fails. **Example:

Python `

class MyClass: pass

obj = MyClass()

try: obj.some_attribute except AttributeError as e: print(e)

`

Output

'MyClass' object has no attribute 'some_attribute'

**Explanation: This code tries to access a non-existent attribute, causing an AttributeError.

9. IndexError

Raised when a sequence subscript is out of range. **Example:

Python `

my_list = [1, 2, 3]

try: element = my_list[5] except IndexError as e: print(e)

`

Output

list index out of range

**Explanation: This code tries to access an out-of-range index in a list, raising an IndexError.

10. KeyError

Raised when a dictionary key is not found. **Example:

Python `

d = {"key1": "value1"}

try: val = d["key2"] except KeyError as e: print(e)

`

**Explanation: This code attempts to access a non-existent dictionary key, causing a KeyError.

11. MemoryError

Raised when an operation runs out of memory. **Example:

Python `

try: li = [1] * (10**10) except MemoryError as e: print(e)

`

**Explanation: This code tries to create a very large list, causing a MemoryError.

12. NameError

Raised when a local or global name is not found. **Example:

Python `

try: print(var) except NameError as e: print(e)

`

Output

name 'var' is not defined

**Explanation: This code attempts to use an undefined variable, raising a NameError.

13. OSError

Raised when a system-related operation (like file I/O) fails. **Example:

Python `

try: open("non_existent_file.txt") except OSError as e: print(e)

`

Output

[Errno 2] No such file or directory: 'non_existent_file.txt'

**Explanation: This code tries to open a non-existent file, causing an OSError.

14. TypeError

Raised when an operation or function is applied to an object of inappropriate type. **Example:

Python `

try: result = '2' + 2 except TypeError as e: print(e)

`

Output

can only concatenate str (not "int") to str

**Explanation: This code tries to add a string and an integer, causing a TypeError.

15. ValueError

Raised when a function receives an argument of the right type but inappropriate value. **Example:

Python `

try: res = int("abc") except ValueError as e: print(e)

`

Output

invalid literal for int() with base 10: 'abc'

**Explanation: This code tries to convert a non-numeric string to an integer, raising a ValueError.

16. ImportError

Raised when an import statement has issues. **Example:

Python `

try: import mod except ImportError as e: print(e)

`

Output

No module named 'mod'

**Explanation: This code attempts to import a non-existent module, causing an ImportError.

17. ModuleNotFoundError

Raised when a module cannot be found. **Example:

Python `

try: import module except ModuleNotFoundError as e: print(e)

`

Output

No module named 'module'

**Explanation: Similar to ImportError, this code tries to import a module that doesn’t exist.

18. IOError

Raised when an I/O operation (like reading or writing to a file) fails. **Example:

Python `

try: open("non_existent_file.txt") except IOError as e: print(e)

`

Output

[Errno 2] No such file or directory: 'non_existent_file.txt'

**Explanation: This is another example of file-related errors, causing an IOError.

19. FileNotFoundError

Raised when a file or directory is requested but cannot be found. **Example:

Python `

try: open("non_existent_file.txt") except FileNotFoundError as e: print(e)

`

Output

[Errno 2] No such file or directory: 'non_existent_file.txt'

**Explanation: This specifically catches the FileNotFoundError when trying to open a missing file.

20. StopIteration

Raised when the next() function is called and there are no more items in an iterator. **Example:

Python `

my_iter = iter([1, 2, 3])

try: while True: print(next(my_iter)) except StopIteration as e: print("End of iterator")

`

Output

1 2 3 End of iterator

**Explanation: This code iterates through a list and raises StopIteration when the list is exhausted.

21. KeyboardInterrupt

Raised when the user presses Ctrl+C or interrupts the program’s execution. **Example:

Python `

try: while True: pass except KeyboardInterrupt as e: print("Program interrupted by user")

`

**Explanation: This code runs an infinite loop until the user interrupts it with Ctrl+C.

22. SystemExit

Raised when the sys.exit() function is called to exit the program. **Example:

Python `

import sys

try: sys.exit() except SystemExit as e: print("System exit called")

`

**Explanation: This code calls sys.exit(), raising a SystemExit exception.

23. NotImplementedError

Raised when an abstract method that needs to be implemented is called. **Example:

Python `

class BaseClass: def some_method(self): raise NotImplementedError("This method should be overridden")

try: obj = BaseClass() obj.some_method() except NotImplementedError as e: print(e)

`

Output

This method should be overridden

**Explanation: This code demonstrates a base class method that should be overridden in subclasses, raising NotImplementedError if called.

24. RuntimeError

Raised when a general error occurs in the program. **Example:

Python `

try: raise RuntimeError("A runtime error occurred") except RuntimeError as e: print(e)

`

Output

A runtime error occurred

**Explanation: This manually raises a RuntimeError and catches it.

25. RecursionError

Raised when the maximum recursion depth is exceeded. **Example:

Python `

try: def recursive_function(): recursive_function()

recursive_function()

except RecursionError as e: print(e)

`

Output

maximum recursion depth exceeded

**Explanation: This code defines a recursive function that calls itself indefinitely, causing a RecursionError.

26. SyntaxError

Raised when there is an error in the syntax of the code. **Example:

Python `

try: eval('x === 2') except SyntaxError as e: print(e)

`

Output

invalid syntax (, line 1)

**Explanation: This code uses eval() to evaluate an incorrect syntax, raising a SyntaxError.

27. IndentationError

Raised when there is an indentation error in the code. **Example:

Python `

try: eval('def func():\n print("Hello")\n print("World")') except IndentationError as e: print(e)

`

**Explanation: This code uses eval() to evaluate code with incorrect indentation, causing an IndentationError.

28. TabError

Raised when the indentation consists of inconsistent use of tabs and spaces. **Example:

Python `

try: eval('def func():\n\tprint("Hello")\n print("World")') except TabError as e: print(e)

`

**Explanation: This code uses eval() to evaluate code with mixed tabs and spaces, causing a TabError.

29. UnicodeError

Raised when a Unicode-related encoding or decoding error occurs. **Example:

Python `

try: 'æ'.encode('ascii') except UnicodeError as e: print(e)

`

Output

'ascii' codec can't encode character '\xe6' in position 0: ordinal not in range(128)

**Explanation: This code tries to encode a non-ASCII character using the ASCII codec, raising a UnicodeError.