Can the python-markdown approximate github markdown by installing extensions?
Mostly yes. Note that GitHub Flavored Markdown (GFM) is built on Commonmark and Python-Markdown is not a Commonmark implementation. Therefore, any differences between Commonmark and the original Markdown rules would need to be addressed by extensions. Those differences are all documented in the Commonmark spec. However, of concern is Commonmark's indentation. It is not likely that Python-Markdown could be adapted to match the exact behavior of the Commonmark spec on this point. That said, for most any "well formed" Markdown, it should be doable.
Then on top of adapting Python-Markdown to Commonmark, you would need extensions to match the various extensions provided by GFM, which are all defined in GitHub's spec (the extensions are all highlighted with a blue background). Note that while Fenced Code Blocks are part of Commonmark, and therefore are not an extension to GFM, they are not part of the original Markdown rules and therefore would require use of the Fenced Code Block extension.
Is there a list of extensions that adds python-markdown the syntax additions from github flavoured markdown ?
I've never seen such a list, which would be off-topic here anyway. That said, you can find a list of all built-in extensions in the Python-Markdown documentation and a list of all known third-party extensions on the project's wiki. I expect you will find extensions which add of of GFM's add-on behavior, but it will be more difficult to find extensions which match Commonmark's base behavior. And the Python-Markdown developers have expressly stated that they are not interested in supporting Commonmark. Any such support would need to come from third party extensions. I expect extensions for most of the differences have not yet been created.
Full disclosure: I am the lead developer of Python-Markdown.
gripis another python package to do the rendering... would they contain some info?