output: optimize obj collection (#6277)

* output: str only once

Calling `__str__` takes a long time and if we are dealing with a large
dataset, it will result in a very substantial time. For example,
locally, for 700K objects, it took 20sec more.

Related to #6276

* output: don't use os.path.join

Takes around 2sec for 700K objects.

* output: use fs.sep

* output: remove unused sep

dvc/fs/base.py

@@ -33,6 +33,8 @@ class RemoteMissingDepsError(DvcException):
 
 
 class BaseFileSystem:
+    sep = "/"
+
     scheme = "base"
     REQUIRES: ClassVar[Dict[str, str]] = {}
     PATH_CLS = URLInfo  # type: Any

dvc/fs/dvc.py

@@ -23,6 +23,8 @@ class DvcFileSystem(BaseFileSystem):  # pylint:disable=abstract-method
         repo: DVC repo.
     """
 
+    sep = os.sep
+
     scheme = "local"
     PARAM_CHECKSUM = "md5"
 

dvc/fs/git.py

@@ -9,6 +9,8 @@
 class GitFileSystem(BaseFileSystem):  # pylint:disable=abstract-method
     """Proxies the repo file access methods to Git objects"""
 
+    sep = os.sep
+
     scheme = "local"
 
     def __init__(self, root_dir, trie):

dvc/fs/local.py

@@ -14,6 +14,8 @@
 
 
 class LocalFileSystem(BaseFileSystem):
+    sep = os.sep
+
     scheme = Schemes.LOCAL
     PATH_CLS = PathInfo
     PARAM_CHECKSUM = "md5"

dvc/fs/repo.py

@@ -31,6 +31,8 @@ class RepoFileSystem(BaseFileSystem):  # pylint:disable=abstract-method
         kwargs: Additional keyword arguments passed to the `DvcFileSystem()`.
     """
 
+    sep = os.sep
+
     scheme = "local"
     PARAM_CHECKSUM = "md5"
 

dvc/output.py

@@ -271,8 +271,6 @@ class Output:
     IsStageFileError = OutputIsStageFileError  # type: Type[DvcException]
     IsIgnoredError = OutputIsIgnoredError  # type: Type[DvcException]
 
-    sep = "/"
-
     def __init__(
         self,
         stage,
@@ -887,7 +885,7 @@ def _set_obj_names(self, obj):
         obj.name = str(self)
         if isinstance(obj, Tree):
             for key, entry_obj in obj:
-                entry_obj.name = os.path.join(str(self), *key)
+                entry_obj.name = self.fs.sep.join([obj.name, *key])
 
     def get_used_external(
         self, **kwargs