#856047: respect the `no_proxy` env var when checking for proxies

in urllib and using the other ``_proxy`` env vars.
Original patch by Donovan Baarda.

Doc/library/urllib.rst

@@ -79,6 +79,11 @@ High-level interface
       % python
       ...
 
+   The :envvar:`no_proxy` environment variable can be used to specify hosts which
+   shouldn't be reached via proxy; if set, it should be a comma-separated list
+   of hostname suffixes, optionally with ``:port`` appended, for example
+   ``cern.ch,ncsa.uiuc.edu,some.host:8080``.
+
    In a Windows environment, if no proxy environment variables are set, proxy
    settings are obtained from the registry's Internet Settings section.
 
@@ -112,6 +117,10 @@ High-level interface
    .. versionchanged:: 2.3
       Added the *proxies* support.
 
+   .. versionchanged:: 2.6
+      Added :meth:`getcode` to returned object and support for the
+      :envvar:`no_proxy` environment variable.
+
 
 .. function:: urlretrieve(url[, filename[, reporthook[, data]]])
 

Lib/urllib.py

@@ -1283,10 +1283,33 @@ def getproxies_environment():
     proxies = {}
     for name, value in os.environ.items():
         name = name.lower()
+        if name == 'no_proxy':
+            # handled in proxy_bypass_environment
+            continue
         if value and name[-6:] == '_proxy':
             proxies[name[:-6]] = value
     return proxies
 
+def proxy_bypass_environment(host):
+    """Test if proxies should not be used for a particular host.
+
+    Checks the environment for a variable named no_proxy, which should
+    be a list of DNS suffixes separated by commas, or '*' for all hosts.
+    """
+    no_proxy = os.environ.get('no_proxy', '') or os.environ.get('NO_PROXY', '')
+    # '*' is special case for always bypass
+    if no_proxy == '*':
+        return 1
+    # strip port off host
+    hostonly, port = splitport(host)
+    # check if the host ends with any of the DNS suffixes
+    for name in no_proxy.split(','):
+        if name and (hostonly.endswith(name) or host.endswith(name)):
+            return 1
+    # otherwise, don't bypass
+    return 0
+
+
 if sys.platform == 'darwin':
     def getproxies_internetconfig():
         """Return a dictionary of scheme -> proxy server URL mappings.
@@ -1314,12 +1337,15 @@ if sys.platform == 'darwin':
                 pass
             else:
                 proxies['http'] = 'http://%s' % value
-        # FTP: XXXX To be done.
-        # Gopher: XXXX To be done.
+        # FTP: XXX To be done.
+        # Gopher: XXX To be done.
         return proxies
 
-    def proxy_bypass(x):
-        return 0
+    def proxy_bypass(host):
+        if getproxies_environment():
+            return proxy_bypass_environment(host)
+        else:
+            return 0
 
     def getproxies():
         return getproxies_environment() or getproxies_internetconfig()
@@ -1379,7 +1405,7 @@ elif os.name == 'nt':
         """
         return getproxies_environment() or getproxies_registry()
 
-    def proxy_bypass(host):
+    def proxy_bypass_registry(host):
         try:
             import _winreg
             import re
@@ -1438,12 +1464,22 @@ elif os.name == 'nt':
                     return 1
         return 0
 
+    def proxy_bypass(host):
+        """Return a dictionary of scheme -> proxy server URL mappings.
+
+        Returns settings gathered from the environment, if specified,
+        or the registry.
+
+        """
+        if getproxies_environment():
+            return proxy_bypass_environment(host)
+        else:
+            return proxy_bypass_registry(host)
+
 else:
     # By default use environment variables
     getproxies = getproxies_environment
-
-    def proxy_bypass(host):
-        return 0
+    proxy_bypass = proxy_bypass_environment
 
 # Test and time quote() and unquote()
 def test1():

Misc/NEWS

@@ -369,6 +369,9 @@ Core and builtins
 Library
 -------
 
+- #856047: respect the ``no_proxy`` environment variable when using the
+  ``http_proxy`` etc. environment variables in urllib.
+
 - #1178141: add a getcode() method to the addinfourls that urllib.open()
   returns so that you can retrieve the HTTP status code.