Comment style: Imperative or third person

For Python, PEP-257 states about docstrings (emphasis added):

The docstring is a phrase ending in a period. It prescribes the function or method's effect as a command ("Do this", "Return that"), not as a description; e.g. don't write "Returns the pathname ...".

And PEP257: Good Python docstring by example is even more explicit (emphasis added):

Note that all docstrings begin with a one-line summary. The summary is written in the imperative mood ("do", "use", "find", "return", "render", etc) and ends with a period.

Oracle's official style guide states:

Use 3rd person (descriptive) not 2nd person (prescriptive). The description is in 3rd person declarative rather than 2nd person imperative.

Gets the label. (preferred)

Get the label. (avoid)

Oracle's style guide can be found here.