avoid import platform

platform module is relatively large: it takes about 5ms to import

requests/sessions.py

@@ -8,7 +8,7 @@ This module provides a Session object to manage and persist settings across
 requests (cookies, auth, proxies).
 """
 import os
-import platform
+import sys
 import time
 from collections import Mapping
 from datetime import timedelta
@@ -38,7 +38,7 @@ from .status_codes import codes
 from .models import REDIRECT_STATI
 
 # Preferred clock, based on which one is more accurate on a given system.
-if platform.system() == 'Windows':
+if sys.platform == 'win32':
     try:  # Python 3.4+
         preferred_clock = time.perf_counter
     except AttributeError:  # Earlier than Python 3.

requests/utils.py

@@ -14,10 +14,10 @@ import collections
 import contextlib
 import io
 import os
-import platform
 import re
 import socket
 import struct
+import sys
 import warnings
 
 from .__version__ import __version__
@@ -39,7 +39,7 @@ NETRC_FILES = ('.netrc', '_netrc')
 DEFAULT_CA_BUNDLE_PATH = certs.where()
 
 
-if platform.system() == 'Windows':
+if sys.platform == 'win32':
     # provide a proxy_bypass version on Windows without DNS lookups
 
     def proxy_bypass_registry(host):