remove list[str] to be compatible with pre py3.8

Author: caesar0301

.github/workflows/python-package.yml

@@ -15,12 +15,12 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@v5.4.0
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies

treelib/tree.py

@@ -742,7 +742,7 @@ def paste(self, nid: str, new_tree, deep: bool = False):
         self.__update_bpointer(new_tree.root, nid)
         self.__update_fpointer(nid, new_tree.root, self.node_class.ADD)
 
-    def paths_to_leaves(self) -> list[list[str]]:
+    def paths_to_leaves(self):
         """
         Use this function to get the identifiers allowing to go from the root
         nodes to each leaf.