Add Deprecation Warnings

[TobyRoseman]

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[znation]

Should we be using the warnings module for this stuff? Note there is a DeprecationWarning there.

[TobyRoseman]

DeprecationWarning is an exception. We don't want to raise an exception (i.e. error out) in these cases.

Using the warning module would probably be better. Although I think a lot of places in our code base currently just use print statements for warnings. We are using the warning module in a few places in the codebase. However we seem to be using logging.warning(...) more. It not clear to me if one is better than the other.

@znation - do you have an option about using warnings.warn(...) vs logging.warning(...)? Since we're using it more, I think logging.warning(...) might be the best option.

[znation]

There is also https://docs.python.org/2.7/library/logging.html#integration-with-the-warnings-module -- which would capture all warnings.warn calls and redirect them to the logger. I think warnings.warn is probably the "right" API for deprecating things in Python, using a DeprecationWarning as an argument to it, rather than raising one), but logging.warning is probably the 2nd best thing to do. Raw print statements is not great since it's harder for users to redirect it (and to redirect it independently of their desired output, like progress tables).

[TobyRoseman]

Sadly warnings.warn("Message", DeprecationWarning) doesn't work in our codebase (the line is executed without error but nothing gets printed). That line does work fine in a standalone script. I suspect it has something to do with how we setup our logging. I'll investigate.

warnings.warn("message") and logging.warn("message") both work fine in our codebase.

[TobyRoseman]

Turns out this issue has nothing to do with our codebase. From the documentation for DeprecationWarning:(ignored by default, unless triggered by code in __main__). That's a very interesting decision, but it explains why it didn't trigger in our codebase but did in a standalone script.

So I don't think warnings.warn with a DeprecationWarning parameter is the right way to go. I'll update this PR to call warnings.warn without a DeprecationWarning parameter. @znation - sounds good?

[znation]

Yes, that sounds good to me, thanks! I am also surprised that deprecation warnings aren't on by default.

[TobyRoseman]

Internal test pass