Comprehensive Examples of Python Exceptions

Here are examples of common Python exceptions with simple programs:

1. SyntaxError

# Missing colon
if True
    print("Hello")

# Missing parenthesis
print("Hello"

2. IndentationError

def my_function():
print("Indented wrong")  # Missing indentation

if True:
    print("Proper")
     print("Wrong indentation")  # Inconsistent indentation

3. NameError

print(undefined_variable)  # Variable not defined

def my_func():
    print(non_existent)

my_func()

4. TypeError

# Adding incompatible types
result = "5" + 3

# Wrong number of arguments
def greet(name):
    return f"Hello {name}"

greet()  # Missing argument

# Invalid operation on type
len(42)  # Integer has no length

5. ValueError

# Invalid conversion
number = int("abc")

# Invalid value for function
float("12.34.56")

# Empty sequence
empty_list = []
value = max(empty_list)

6. IndexError

my_list = [1, 2, 3]
print(my_list[5])  # Index out of range

empty_list = []
print(empty_list[0])  # No elements

7. KeyError

my_dict = {"name": "John", "age": 25}
print(my_dict["address"])  # Key doesn't exist

empty_dict = {}
print(empty_dict["any_key"])

8. ZeroDivisionError

result = 10 / 0

numbers = [1, 0, 2]
for num in numbers:
    print(5 / num)  # Will fail when num is 0

9. FileNotFoundError

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

import os
os.remove("file_that_doesnt_exist.txt")

10. PermissionError

# Try to write to a read-only file (create a read-only file first)
with open("read_only_file.txt", "w") as file:
    file.write("test")

11. ImportError

import non_existent_module

from math import non_existent_function

12. AttributeError

x = 5
x.append(10)  # Integer has no append method

class MyClass:
    pass

obj = MyClass()
obj.undefined_method()

13. RuntimeError

# Custom runtime error
def problematic_function():
    raise RuntimeError("Something went wrong!")

problematic_function()

14. RecursionError

def infinite_recursion():
    return infinite_recursion()

infinite_recursion()  # Maximum recursion depth exceeded

15. KeyboardInterrupt

# Run this and press Ctrl+C
try:
    while True:
        pass
except KeyboardInterrupt:
    print("Program interrupted by user!")

16. MemoryError

# This may cause MemoryError on systems with limited memory
try:
    huge_list = [0] * (10**10)
except MemoryError:
    print("Out of memory!")

17. OverflowError

import math
try:
    result = math.exp(1000)  # Too large for float
except OverflowError:
    print("Number too large!")

18. StopIteration

iterator = iter([1, 2])
print(next(iterator))  # 1
print(next(iterator))  # 2
print(next(iterator))  # Raises StopIteration

19. AssertionError

x = 5
assert x == 10, "x should be 10"  # Assertion fails

def divide(a, b):
    assert b != 0, "Cannot divide by zero"
    return a / b

divide(10, 0)

20. UnboundLocalError

x = 10

def my_function():
    print(x)  # This would work
    x = 5     # But this makes x local

my_function()  # UnboundLocalError

21. ModuleNotFoundError

try:
    import non_existent_package
except ModuleNotFoundError as e:
    print(f"Module not found: {e}")

22. TimeoutError

import socket
socket.setdefaulttimeout(0.0001)
try:
    socket.getaddrinfo("example.com", 80)
except TimeoutError:
    print("Connection timed out")

23. NotImplementedError

class AbstractClass:
    def must_implement(self):
        raise NotImplementedError("Subclasses must implement this method")

class ConcreteClass(AbstractClass):
    pass  # Forgot to implement the method

obj = ConcreteClass()
obj.must_implement()

24. Complete Example with Multiple Exceptions

def demonstrate_exceptions():
    exceptions = [
        ("NameError", lambda: print(undefined_var)),
        ("TypeError", lambda: "5" + 3),
        ("IndexError", lambda: [1, 2, 3][10]),
        ("KeyError", lambda: {"a": 1}["b"]),
        ("ZeroDivisionError", lambda: 10 / 0),
        ("ValueError", lambda: int("abc")),
    ]

    for name, func in exceptions:
        try:
            func()
        except Exception as e:
            print(f"{name}: {type(e).__name__} - {e}")

demonstrate_exceptions()

25. Custom Exception

class CustomError(Exception):
    def __init__(self, message):
        self.message = message
        super().__init__(self.message)

def validate_age(age):
    if age < 0:
        raise CustomError("Age cannot be negative!")
    if age > 150:
        raise CustomError("Age seems unrealistic!")
    return True

try:
    validate_age(-5)
except CustomError as e:
    print(f"Custom error: {e}")

26. Multiple Exception Handling

def handle_multiple_errors():
    try:
        # This will cause different errors based on input
        num = int(input("Enter a number: "))
        result = 100 / num
        print(f"100 divided by {num} is {result}")

    except ValueError:
        print("Please enter a valid integer!")
    except ZeroDivisionError:
        print("Cannot divide by zero!")
    except Exception as e:
        print(f"Unexpected error: {e}")

handle_multiple_errors()

These examples demonstrate the most common exceptions you’ll encounter in Python programming. Each exception serves as a specific signal about what went wrong in your code.