Use "yield from" syntax

Available since Python 3.3.

https://docs.python.org/3/whatsnew/3.3.html#pep-380

src/pip/_internal/network/session.py

@@ -340,8 +340,7 @@ class PipSession(requests.Session):
 
     def iter_secure_origins(self):
         # type: () -> Iterator[SecureOrigin]
-        for secure_origin in SECURE_ORIGINS:
-            yield secure_origin
+        yield from SECURE_ORIGINS
         for host, port in self.pip_trusted_origins:
             yield ('*', host, '*' if port is None else port)
 

src/pip/_internal/req/req_file.py

@@ -334,8 +334,7 @@ class RequirementsFileParser:
         # type: (str, bool) -> Iterator[ParsedLine]
         """Parse a given file, yielding parsed lines.
         """
-        for line in self._parse_and_recurse(filename, constraint):
-            yield line
+        yield from self._parse_and_recurse(filename, constraint)
 
     def _parse_and_recurse(self, filename, constraint):
         # type: (str, bool) -> Iterator[ParsedLine]
@@ -363,10 +362,7 @@ class RequirementsFileParser:
                         os.path.dirname(filename), req_path,
                     )
 
-                for inner_line in self._parse_and_recurse(
-                    req_path, nested_constraint,
-                ):
-                    yield inner_line
+                yield from self._parse_and_recurse(req_path, nested_constraint)
             else:
                 yield line