bpo-29585: optimize site.py startup time (GH-136)

Avoid importing `sysconfig` from `site` by copying minimum code.
Python startup is 5% faster on Linux and 30% faster on macOS

1 files changed, 10 insertions, 16 deletions

diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py
index ed0a34d..e6618b1 100644
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -51,6 +51,7 @@ _INSTALL_SCHEMES = {
         'scripts': '{base}/Scripts',
         'data': '{base}',
         },
+    # NOTE: When modifying "purelib" scheme, update site._get_path() too.
     'nt_user': {
         'stdlib': '{userbase}/Python{py_version_nodot}',
         'platstdlib': '{userbase}/Python{py_version_nodot}',
@@ -177,32 +178,25 @@ def _get_default_scheme():
     return os.name
 
 
+# NOTE: site.py has copy of this function.
+# Sync it when modify this function.
 def _getuserbase():
     env_base = os.environ.get("PYTHONUSERBASE", None)
+    if env_base:
+        return env_base
 
     def joinuser(*args):
         return os.path.expanduser(os.path.join(*args))
 
     if os.name == "nt":
         base = os.environ.get("APPDATA") or "~"
-        if env_base:
-            return env_base
-        else:
-            return joinuser(base, "Python")
+        return joinuser(base, "Python")
 
-    if sys.platform == "darwin":
-        framework = get_config_var("PYTHONFRAMEWORK")
-        if framework:
-            if env_base:
-                return env_base
-            else:
-                return joinuser("~", "Library", framework, "%d.%d" %
-                                sys.version_info[:2])
+    if sys.platform == "darwin" and sys._framework:
+        return joinuser("~", "Library", sys._framework,
+                        "%d.%d" % sys.version_info[:2])
 
-    if env_base:
-        return env_base
-    else:
-        return joinuser("~", ".local")
+    return joinuser("~", ".local")
 
 
 def _parse_makefile(filename, vars=None):