collection: performance: use optimized parts function

Time: 8.53s => 5.73s

src/_pytest/main.py

@@ -18,6 +18,7 @@ from _pytest.config import directory_arg
 from _pytest.config import hookimpl
 from _pytest.config import UsageError
 from _pytest.outcomes import exit
+from _pytest.pathlib import parts
 from _pytest.runner import collect_one_node
 
 
@@ -469,8 +470,8 @@ class Session(nodes.FSCollector):
             return items
 
     def collect(self):
-        for parts in self._initialparts:
-            arg = "::".join(map(str, parts))
+        for initialpart in self._initialparts:
+            arg = "::".join(map(str, initialpart))
             self.trace("processing argument", arg)
             self.trace.root.indent += 1
             try:
@@ -532,12 +533,12 @@ class Session(nodes.FSCollector):
                 fil=filter_, rec=self._recurse, bf=True, sort=True
             ):
                 pkginit = path.dirpath().join("__init__.py")
-                if pkginit.exists() and not any(x in pkginit.parts() for x in paths):
+                if pkginit.exists() and not any(x in parts(pkginit.strpath) for x in paths):
                     for x in root._collectfile(pkginit):
                         yield x
                         paths.append(x.fspath.dirpath())
 
-                if not any(x in path.parts() for x in paths):
+                if not any(x in parts(path.strpath) for x in paths):
                     for x in root._collectfile(path):
                         if (type(x), x.fspath) in self._node_cache:
                             yield self._node_cache[(type(x), x.fspath)]

src/_pytest/pathlib.py

@@ -303,3 +303,8 @@ def fnmatch_ex(pattern, path):
     else:
         name = six.text_type(path)
     return fnmatch.fnmatch(name, pattern)
+
+
+def parts(s):
+    parts = s.split(sep)
+    return [sep.join(parts[:i+1]) or sep for i in range(len(parts))]

src/_pytest/python.py

@@ -41,6 +41,7 @@ from _pytest.mark.structures import get_unpacked_marks
 from _pytest.mark.structures import normalize_mark_list
 from _pytest.mark.structures import transfer_markers
 from _pytest.outcomes import fail
+from _pytest.pathlib import parts
 from _pytest.warning_types import PytestWarning
 from _pytest.warning_types import RemovedInPytest4Warning
 
@@ -562,14 +563,10 @@ class Package(Module):
             yield Module(init_module, self)
         pkg_prefixes = set()
         for path in this_path.visit(rec=self._recurse, bf=True, sort=True):
-            # We will visit our own __init__.py file, in which case we skip it.
-            if path.isfile():
-                if path.basename == "__init__.py" and path.dirpath() == this_path:
-                    continue
 
-            parts = path.parts()
+            parts_ = parts(path.strpath)
             if any(
-                pkg_prefix in parts and pkg_prefix.join("__init__.py") != path
+                pkg_prefix in parts_ and pkg_prefix.join("__init__.py") != path
                 for pkg_prefix in pkg_prefixes
             ):
                 continue