code: def resolve_requirement_strings(self, interpreter, requirement_strings):
      
      requirement_strings = sorted(requirement_strings)
      if len(requirement_strings) == 0:
        req_strings_id = 'no_requirements'
      elif len(requirement_strings) == 1:
        req_strings_id = requirement_strings[0]
      else:
        req_strings_id = hash_all(requirement_strings)
  
      path = os.path.realpath(os.path.join(self.workdir, str(interpreter.identity), req_strings_id))
      if not os.path.isdir(path):
        reqs = [PythonRequirement(req_str) for req_str in requirement_strings]
        with safe_concurrent_creation(path) as safe_path:
          pex_builder = PexBuilderWrapper.Factory.create(
            builder=PEXBuilder(path=safe_path, interpreter=interpreter, copy=True),
            log=self.context.log)
          pex_builder.add_resolved_requirements(reqs)
          pex_builder.freeze()
      return PEX(path, interpreter=interpreter)
docs: Resolve a list of pip-style requirement strings.