I think/assume that the syntax specifying versions is the one documented at Package match specifications.
So you would write - numpy >=1.2.3,<1.3
(space after numpy, no space after the comma – not tested).
BTW, I couldn’t find any documentation describing the structure of the environment file environment.yml
. creating-an-environment-from-an-environment-yml-file refers to Creating an environment file manually and vice-versa.