code: def prepare_installed_requirement(self, req, require_hashes, skip_reason):
          # type: (InstallRequirement, bool, Optional[str]) -> DistAbstraction
          
          assert req.satisfied_by, "req should have been satisfied but isn't"
          assert skip_reason is not None, (
              "did not get skip reason skipped but req.satisfied_by "
              "is set to %r" % (req.satisfied_by,)
          )
          logger.info(
              'Requirement %s: %s (%s)',
              skip_reason, req, req.satisfied_by.version
          )
          with indent_log():
              if require_hashes:
                  logger.debug(
                      'Since it is already installed, we are trusting this '
                      'package without checking its hash. To ensure a '
                      'completely repeatable environment, install into an '
                      'empty virtualenv.'
                  )
              abstract_dist = Installed(req)
  
          return abstract_dist
docs: Prepare an already-installed requirement