Why does PyYAML 5.1 raise YAMLLoadWarning when the default loader has been made safer already?

Here is my code:

import yaml
yaml.load('foo')

This code leads to the following warning with PyYAML (5.1).

$ pip install pyyaml
$ python3 foo.py
foo.py:2: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
  yaml.load('foo')

So I visited https://msg.pyyaml.org/load to see what this is about but I do not understand the need for this warning.

First, the documentation says,

UnsafeLoader (also called Loader for backwards compatability)

The original Loader code that could be easily exploitable by untrusted data input.

Okay, that makes sense. In an earlier version, the original loader was unsafe. Further, it says,

FullLoader

Loads the full YAML language. Avoids arbitrary code execution. This is currently (PyYAML 5.1) the default loader called by yaml.load(input) (after issuing the warning).

So the current version uses FullLoader which is not unsafe. This is confirmed again in the document.

The load function was also made much safer by disallowing the execution of arbitrary functions by the default loader (FullLoader).

If the current version that uses FullLoader is not unsafe, then why do we need the YAMLLoadWarning at all?

[slavaGanzin]

Explicit is better than implicit.

I just want my YAML loaded. I don’t care about best practices, moral views of creators and other unrelated stuff. You made it more secure? Awesome, good job. But make changes unnoticeable: set securest loader by default. It’s service library and it should make things done and not “educate users”.

And if you like to cite principles, here is one for you too: https://en.wikipedia.org/wiki/Open–closed_principle

[rpuntaie]

Flectra has a problem with pyyaml 5.1, which would not need to be. I just changed =Loader to =FullLoader consistently in __init__() and then flectra works with 5.1. Why the change in only load() to make it inconsistent with the other functions in __init__.py?

I would suggest some tests that test the interface of pyyaml as a whole, i.e. the interoperability of the functions, like add_constructor() and load(). Use these tests to verify that changes do not change the interface. Interface changes do produce a lot of effort. We’ve seen this with the Python 3 move.

I wonder whether semantic versioning is the right way to go at all. New interfaces should rather be handled via a new name and be installable in parallel. So we would have pyyaml5 1.0 instead of pyyaml 5.1.0. In code we would do import yaml5 instead of import yaml.