📚 Python Built-in Exceptions – Master Error Types & Their Use

🧲 Introduction – Why Learn Built-in Exceptions?

When your Python program crashes with messages like IndexError, TypeError, or ZeroDivisionError, it’s not random—it’s Python raising a built-in exception.

Understanding these built-in exceptions helps you:

• Write cleaner, more defensive code
• Debug faster
• Handle errors gracefully with try...except

🎯 In this guide, you’ll learn:

• What built-in exceptions are in Python
• The most common exception types
• Their real-world causes and fixes
• How to use try...except to handle them
• Best practices for robust error handling

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✅ What Are Built-in Exceptions?

Built-in exceptions are standard error types raised by Python automatically when something goes wrong.

🔧 These exceptions are all subclasses of the built-in Exception class.

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🧾 Most Common Built-in Exceptions

Here’s a quick table of frequently encountered exceptions:

Exception	Trigger Condition	Example
ZeroDivisionError	Division by zero	1 / 0
ValueError	Invalid value for a function	int("abc")
TypeError	Wrong data type used	"2" + 2
IndexError	List index out of range	mylist[100]
KeyError	Missing key in dict	mydict["xyz"]
FileNotFoundError	File doesn’t exist	open("missing.txt")
AttributeError	Object has no attribute	None.upper()
ImportError	Module cannot be found	import fake_module
IndentationError	Improper indentation	wrong tab/space usage
NameError	Undefined variable used	print(x) (x not defined)

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🔁 Example: Handling Built-in Exceptions

✅ ZeroDivisionError

try:
    result = 10 / 0
except ZeroDivisionError:
    print("❌ You can't divide by zero.")

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✅ ValueError

try:
    age = int("twenty")
except ValueError:
    print("❌ Invalid input. Please enter a number.")

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✅ FileNotFoundError

try:
    with open("data.txt", "r") as f:
        print(f.read())
except FileNotFoundError:
    print("❌ The file does not exist.")

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🧠 Less Common but Important Exceptions

Exception	When It Happens
MemoryError	System runs out of memory
OverflowError	Result too large for data type
EOFError	Input ends unexpectedly
RuntimeError	Unspecified internal issue
StopIteration	Raised by next() in iterators
AssertionError	assert statement fails

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⚠️ Special Exceptions (Subclass of BaseException)

Exception	Description
SystemExit	Raised when sys.exit() is called
KeyboardInterrupt	When you press Ctrl+C
GeneratorExit	Raised when a generator is closed

💡 These should rarely be caught unless necessary.

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📘 Best Practices

💡 Practice	Why It’s Important
Catch specific exceptions	Avoids hiding bugs
Use finally for cleanup	Ensures resource release
Avoid catching Exception broadly	Can suppress real problems
Always log exception details	Helpful for debugging

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💡 Tip: View All Built-in Exceptions

import builtins
print(dir(builtins))

You’ll see exceptions like ArithmeticError, LookupError, PermissionError, etc.

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📌 Summary – Recap & Next Steps

Python has dozens of built-in exceptions to handle invalid inputs, missing files, runtime logic errors, and more.

🔍 Key Takeaways:

• ✅ Built-in exceptions are raised automatically by Python
• ✅ Handle them using try...except for clean recovery
• ✅ Know the difference between common ones like ValueError, TypeError, and KeyError
• ⚠️ Avoid overly broad except: clauses—catch specific errors instead

⚙️ Real-World Relevance:
Mastering built-in exceptions is essential for stable scripting, debugging, API development, and robust application design.

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❓ FAQ – Python Built-in Exceptions

❓ How many built-in exceptions are there?

✅ Python has 60+ built-in exceptions. You can see them via:

help("exceptions")

❓ What is the parent of all exceptions?

✅ All exceptions inherit from the base class Exception, which itself inherits from BaseException.

❓ Can I catch multiple exceptions in one block?

✅ Yes:

except (ValueError, TypeError) as e:
    print(e)

❓ Should I catch BaseException?

❌ No. Catch only Exception or its subclasses. Catching BaseException also catches SystemExit and KeyboardInterrupt, which should usually terminate the program.

❓ What’s the difference between IndexError and KeyError?

• IndexError: List/tuple index is out of range.
• KeyError: Dictionary key doesn’t exist.

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