[3.10] gh-91539: improve performance of get_proxies_environment (GH-91566)

Lib/urllib/request.py

@@ -2492,28 +2492,34 @@ def getproxies_environment():
  this seems to be the standard convention. If you need a
  different way, you can pass a proxies dictionary to the
  [Fancy]URLopener constructor.
-
  """
- proxies = {}
  # in order to prefer lowercase variables, process environment in
  # two passes: first matches any, second pass matches lowercase only
- for name, value in os.environ.items():
- name = name.lower()
- if value and name[-6:] == '_proxy':
- proxies[name[:-6]] = value
+
+ # select only environment variables which end in (after making lowercase) _proxy
+ proxies = {}
+ environment = []
+ for name in os.environ.keys():
+ # fast screen underscore position before more expensive case-folding
+ if len(name) > 5 and name[-6] == "_" and name[-5:].lower() == "proxy":
+ value = os.environ[name]
+ proxy_name = name[:-6].lower()
+ environment.append((name, value, proxy_name))
+ if value:
+ proxies[proxy_name] = value
  # CVE-2016-1000110 - If we are running as CGI script, forget HTTP_PROXY
  # (non-all-lowercase) as it may be set from the web server by a "Proxy:"
  # header from the client
  # If "proxy" is lowercase, it will still be used thanks to the next block
  if 'REQUEST_METHOD' in os.environ:
  proxies.pop('http', None)
- for name, value in os.environ.items():
+ for name, value, proxy_name in environment:
+ # not case-folded, checking here for lower-case env vars only
  if name[-6:] == '_proxy':
- name = name.lower()
  if value:
- proxies[name[:-6]] = value
+ proxies[proxy_name] = value
  else:
- proxies.pop(name[:-6], None)
+ proxies.pop(proxy_name, None)
  return proxies
 
 def proxy_bypass_environment(host, proxies=None):

Misc/NEWS.d/next/Library/2022-04-15-11-29-38.gh-issue-91539.7WgVuA.rst

@@ -0,0 +1 @@
+Improve performance of ``urllib.request.getproxies_environment`` when there are many environment variables