如何列出Python 3.x模块可抛出的预设错误类型？

Hey Andre, great question! Building a logging system that captures specific exceptions to clarify error types is a fantastic approach for debugging and monitoring. Here are several practical ways to discover the exception types a given module can raise—no source code diving or intentional crashes required:

1. List Exception Classes with dir() #

Most modules group their exceptions in a submodule (often named exc or exceptions). You can use Python's built-in dir() function to filter for classes that end with "Error" (a common naming convention for exceptions):

# Example for SQLAlchemy (where IntegrityError lives)
import sqlalchemy.exc
print([item for item in dir(sqlalchemy.exc) if item.endswith('Error')])

This will output a list of all error-related classes in the module, like IntegrityError, OperationalError, and ProgrammingError.

2. Use the __all__ Attribute #

Many well-designed modules explicitly list their public exceptions in the __all__ attribute of their exception submodule. This gives you a curated list of exceptions the module intends for external use:

from sqlalchemy import exc
print(exc.__all__)

The output will include all public exceptions, making it easy to identify which ones you should handle in your logging.

3. Get Detailed Context with help() #

Once you've identified an exception name (like IntegrityError), use the help() function to learn what triggers it and what it represents—no source code needed:

help(sqlalchemy.exc.IntegrityError)

This will print a full description of the exception, including its purpose, inheritance hierarchy, and common scenarios where it's raised (e.g., database constraint violations for IntegrityError). You can also run help(sqlalchemy.exc) to get an overview of all exceptions in the submodule.

4. Access Module Documentation via pydoc #

If you want structured, official details without leaving your terminal, use Python's pydoc tool. For example, running this command will display a full breakdown of SQLAlchemy's exception classes:

pydoc sqlalchemy.exc

Most popular modules (database libraries, HTTP clients, etc.) use this tool to document their exceptions, including when each one is raised and how to handle it.

Quick Example for Your Use Case #

If you're working with a database module that raises IntegrityError, the above steps will confirm its existence, show you related exceptions, and explain it triggers when a database integrity constraint is violated (like a duplicate primary key). This lets you confidently add except IntegrityError: blocks to your code and log those errors with specific, actionable context.

内容的提问来源于stack exchange，提问作者Chicrala