Maybe send this instruction below the 'dir_path' condition code since it's unused in it.

Why do you need to do explicitely the condition code on the variable dir_path?

Adapting the existing code with the dir_path renamed was ok, i think.

return redirect(url_for('browse_revision_directory',
                return redirect(url_for('browse_revision_directory',
                                        sha1_git=sha1_git,
                                        dir_path=data.get('dir_path')))

Sorry, i mistyped. I meant, this should be enough, shouldn't it?

return redirect(url_for('browse_revision_directory',
                                       sha1_git=sha1_git,
                                       dir_path=data.get('dir_path')))

Empty GET params (like path) are empty strings when I receive them. This was to avoid giving an empty string to url_for, which would build an incorrect url for the redirect. It's factorized and more legible now :)