Is it OK to inspect properties beginning with underscore?

Question

I've been working on a very simple crud generator for pylons. I came up with something that inspects

SomeClass._sa_class_manager.mapper.c

Is it ok to inspect this (or to call methods begining with underscore)? I always kind of assumed this is legal though frowned upon as it relies heavily on the internal structure of a class/object. But hey, since python does not really have interfaces in the Java sense maybe it is OK.

Answer 1

It is intentional (in Python) that there are no "private" scopes. It is a convention that anything that starts with an underscore should not ideally be used, and hence you may not complain if its behavior or definition changes in a next version.

Answer 2

In general, this usually indicates that the method is effectively internal, rather than part of the documented interface, and should not be relied on. Future versions of the library are free to rename or remove such methods, so if you care about future compatability without having to rewrite, avoid doing it.

Answer 3

If it works, why not? You could have problems though when _sa_class_manager gets restructured, binding yourself to this specific version of SQLAlchemy, or creating more work to track the changes. As SQLAlchemy is a fast moving target, you may be there in a year already.

The preferable way would be to integrate your desired API into SQLAlchemy itself.

Answer 4

It's generally not a good idea, for reasons already mentioned. However, Python deliberately allows this behaviour in case there is no other way of doing something.

For example, if you have a closed-source compiled Python library where the author didn't think you'd need direct access to a certain object's internal state—but you really do—you can still get at the information you need. You have the same problems mentioned before of keeping up with different versions (if you're lucky enough that it's still maintained) but at least you can actually do what you wanted to do.