Move Downloader to network.download

This will help us move Downloader construction out of
RequirementPreparer, reducing its concerns and making it easier to test
in isolation.

Author: chrahunt

src/pip/_internal/network/download.py

@@ -5,6 +5,7 @@
 import mimetypes
 import os
 
+from pip._vendor import requests
 from pip._vendor.requests.models import CONTENT_CHUNK_SIZE
 
 from pip._internal.models.index import PyPI
@@ -157,3 +158,43 @@ def _http_get_download(session, link):
     )
     resp.raise_for_status()
     return resp
+
+
+class Download(object):
+    def __init__(
+        self,
+        response,  # type: Response
+        filename,  # type: str
+        chunks,  # type: Iterable[bytes]
+    ):
+        # type: (...) -> None
+        self.response = response
+        self.filename = filename
+        self.chunks = chunks
+
+
+class Downloader(object):
+    def __init__(
+        self,
+        session,  # type: PipSession
+        progress_bar,  # type: str
+    ):
+        # type: (...) -> None
+        self._session = session
+        self._progress_bar = progress_bar
+
+    def __call__(self, link):
+        # type: (Link) -> Download
+        try:
+            resp = _http_get_download(self._session, link)
+        except requests.HTTPError as e:
+            logger.critical(
+                "HTTP error %s while getting %s", e.response.status_code, link
+            )
+            raise
+
+        return Download(
+            resp,
+            _get_http_response_filename(resp, link),
+            _prepare_download(resp, link, self._progress_bar),
+        )

src/pip/_internal/operations/prepare.py

@@ -12,7 +12,6 @@
 import sys
 
 from pip._vendor import requests
-from pip._vendor.requests.models import Response
 from pip._vendor.six import PY2
 
 from pip._internal.distributions import (
@@ -27,11 +26,7 @@
     PreviousBuildDirError,
     VcsHashUnsupported,
 )
-from pip._internal.network.download import (
-    _get_http_response_filename,
-    _http_get_download,
-    _prepare_download,
-)
+from pip._internal.network.download import Downloader
 from pip._internal.utils.compat import expanduser
 from pip._internal.utils.filesystem import copy2_fixed
 from pip._internal.utils.hashes import MissingHashes
@@ -53,7 +48,7 @@
 
 if MYPY_CHECK_RUNNING:
     from typing import (
-        Callable, Iterable, List, Optional, Tuple,
+        Callable, List, Optional, Tuple,
     )
 
     from mypy_extensions import TypedDict
@@ -307,46 +302,6 @@ def unpack_url(
         )
 
 
-class Download(object):
-    def __init__(
-        self,
-        response,  # type: Response
-        filename,  # type: str
-        chunks,  # type: Iterable[bytes]
-    ):
-        # type: (...) -> None
-        self.response = response
-        self.filename = filename
-        self.chunks = chunks
-
-
-class Downloader(object):
-    def __init__(
-        self,
-        session,  # type: PipSession
-        progress_bar,  # type: str
-    ):
-        # type: (...) -> None
-        self._session = session
-        self._progress_bar = progress_bar
-
-    def __call__(self, link):
-        # type: (Link) -> Download
-        try:
-            resp = _http_get_download(self._session, link)
-        except requests.HTTPError as e:
-            logger.critical(
-                "HTTP error %s while getting %s", e.response.status_code, link
-            )
-            raise
-
-        return Download(
-            resp,
-            _get_http_response_filename(resp, link),
-            _prepare_download(resp, link, self._progress_bar),
-        )
-
-
 def _download_http_url(
     link,  # type: Link
     downloader,  # type: Downloader