optimize code for proxy handling of `urllib.request`

[NewUserHa]

Feature or enhancement

Proposal:

1. the second loop of line starts from 1845 is duplicated from the first loop.
   

   cpython/Lib/urllib/request.py

   Lines 1817 to 1853 in 2041a95

   	# Proxy handling
   	def getproxies_environment():
   	"""Return a dictionary of scheme -> proxy server URL mappings.
   	Scan the environment for variables named <scheme>_proxy;
   	this seems to be the standard convention.
   	"""
   	# in order to prefer lowercase variables, process environment in
   	# two passes: first matches any, second pass matches lowercase only
   	# select only environment variables which end in (after making lowercase) _proxy
   	proxies = {}
   	environment = []
   	for name in os.environ:
   	# 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, proxy_name in environment:
   	# not case-folded, checking here for lower-case env vars only
   	if name[-6:] == '_proxy':
   	if value:
   	proxies[proxy_name] = value
   	else:
   	proxies.pop(proxy_name, None)
   	return proxies

2. the registry access should be separated to a standalone function for cache, to be used by code like https://github.com/aio-libs/aiohttp/blob/e79b2d5df70a2644e81925cc49558962af91848d/aiohttp/client.py#L609-L617
   

   cpython/Lib/urllib/request.py

   Lines 2071 to 2104 in 2041a95

   	def proxy_bypass_registry(host):
   	try:
   	import winreg
   	except ImportError:
   	# Std modules, so should be around - but you never know!
   	return False
   	try:
   	internetSettings = winreg.OpenKey(winreg.HKEY_CURRENT_USER,
   	r'Software\Microsoft\Windows\CurrentVersion\Internet Settings')
   	proxyEnable = winreg.QueryValueEx(internetSettings,
   	'ProxyEnable')[0]
   	proxyOverride = str(winreg.QueryValueEx(internetSettings,
   	'ProxyOverride')[0])
   	# ^^^^ Returned as Unicode but problems if not converted to ASCII
   	except OSError:
   	return False
   	if not proxyEnable or not proxyOverride:
   	return False
   	return _proxy_bypass_winreg_override(host, proxyOverride)
   	def proxy_bypass(host):
   	"""Return True, if host should be bypassed.
   	Checks proxy settings gathered from the environment, if specified,
   	or the registry.
   	"""
   	proxies = getproxies_environment()
   	if proxies:
   	return proxy_bypass_environment(host, proxies)
   	else:
   	return proxy_bypass_registry(host)

3. the proxy setting from registry should be ignored when if proxies from environment exists? like the proxy_bypass()

Should open a PR?

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-127753: make the proxies handling of urllib.request cacheable  #127767

[srinivasreddy]

I would like to take it, if not taken?