Simplify `command.easy_install.get_site_dirs`

setuptools/command/easy_install.py

@@ -1371,51 +1371,56 @@ def get_site_dirs():
     if sys.exec_prefix != sys.prefix:
         prefixes.append(sys.exec_prefix)
     for prefix in prefixes:
-        if prefix:
-            if sys.platform in ('os2emx', 'riscos'):
-                sitedirs.append(os.path.join(prefix, "Lib", "site-packages"))
-            elif os.sep == '/':
-                sitedirs.extend([
-                    os.path.join(
-                        prefix,
-                        "lib",
-                        "python{}.{}".format(*sys.version_info),
-                        "site-packages",
-                    ),
-                    os.path.join(prefix, "lib", "site-python"),
-                ])
-            else:
-                sitedirs.extend([
+        if not prefix:
+            continue
+
+        if sys.platform in ('os2emx', 'riscos'):
+            sitedirs.append(os.path.join(prefix, "Lib", "site-packages"))
+        elif os.sep == '/':
+            sitedirs.extend([
+                os.path.join(
                     prefix,
-                    os.path.join(prefix, "lib", "site-packages"),
-                ])
-            if sys.platform == 'darwin':
-                # for framework builds *only* we add the standard Apple
-                # locations. Currently only per-user, but /Library and
-                # /Network/Library could be added too
-                if 'Python.framework' in prefix:
-                    home = os.environ.get('HOME')
-                    if home:
-                        home_sp = os.path.join(
-                            home,
-                            'Library',
-                            'Python',
-                            '{}.{}'.format(*sys.version_info),
-                            'site-packages',
-                        )
-                        sitedirs.append(home_sp)
+                    "lib",
+                    "python{}.{}".format(*sys.version_info),
+                    "site-packages",
+                ),
+                os.path.join(prefix, "lib", "site-python"),
+            ])
+        else:
+            sitedirs.extend([
+                prefix,
+                os.path.join(prefix, "lib", "site-packages"),
+            ])
+        if sys.platform != 'darwin':
+            continue
+
+        # for framework builds *only* we add the standard Apple
+        # locations. Currently only per-user, but /Library and
+        # /Network/Library could be added too
+        if 'Python.framework' not in prefix:
+            continue
+
+        home = os.environ.get('HOME')
+        if not home:
+            continue
+
+        home_sp = os.path.join(
+            home,
+            'Library',
+            'Python',
+            '{}.{}'.format(*sys.version_info),
+            'site-packages',
+        )
+        sitedirs.append(home_sp)
     lib_paths = get_path('purelib'), get_path('platlib')
-    for site_lib in lib_paths:
-        if site_lib not in sitedirs:
-            sitedirs.append(site_lib)
+
+    sitedirs.extend(s for s in lib_paths if s not in sitedirs)
 
     if site.ENABLE_USER_SITE:
         sitedirs.append(site.USER_SITE)
 
-    try:
+    with contextlib.suppress(AttributeError):
         sitedirs.extend(site.getsitepackages())
-    except AttributeError:
-        pass
 
     sitedirs = list(map(normalize_path, sitedirs))