Master Python Exception Handling: From Basics to Advanced Techniques

This article is a note‑style summary after learning Python exceptions, not a comprehensive guide.

1. Python Exception Classes

Python is an object‑oriented language, so exceptions are classes. Common built‑in exception types are listed.

2. Catching Exceptions

The full syntax of try…except…else…finally is shown.

You can omit else, finally, or even the exception clause.

2.1 try…except

Explanation of the try suite and except block. Simplest form shown.

To handle specific exceptions, pass the exception class to except.

Example catching ZeroDivisionError.

Multiple exceptions can be handled by passing a tuple or using multiple except clauses (image).

The except argument is an exception instance providing diagnostic information.

2.2 try…except…else

else runs when no exception occurs; example shown.

2.3 finally

finally runs regardless of exception; can be used alone or with except/else. Example demonstrates all four clauses together.

3. Two Convenient Exception‑Handling Shortcuts

3.1 assert

Syntax of assert shown.

assert evaluates an expression and raises AssertionError with an optional message if false; it can be caught by try.

3.2 with statement (context manager)

with simplifies resource management. Syntax shown.

Example opens a file, iterates its lines, and automatically closes the file.

Only objects implementing the context‑management protocol can be used; examples include file, decimal.Context, thread.LockType, threading.Lock, threading.RLock, threading.Condition, threading.Semaphore, threading.BoundedSemaphore.

4. Raising Exceptions

raise can actively raise an exception. Basic syntax shown.

First argument must be an exception class or instance; second argument is a tuple of parameters; third argument traceback is rarely used. Several examples illustrated.

5. Exceptions and the sys Module

sys.exc_info() returns a tuple (exception type, exception instance, traceback).