prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Join operation in trees---not handling label_attribute
  <!-- If you have a general question about NetworkX, please use the discussions tab to create a new discussion -->
  
  <!--- Provide a general summary of the issue in the Title above -->
  [https://github.com/networkx/networkx/blob/main/networkx/algorithms/tree/operations.py](https://github.com/networkx/networkx/blob/main/networkx/algorithms/tree/operations.py)
  1. The resulting graph of join operation in trees isn't including the old labels of inputs.
  2.  Not handling the cases where label_attribute is passed as an argument.
  
  ### Current Behavior
  ![Screenshot from 2023-03-11 17-03-33](https://user-images.githubusercontent.com/88175932/224483929-b1ebff93-2e5e-46a6-9c6e-11de1dc53ca1.png)
  
  <!--- Tell us what happens instead of the expected behavior -->
  
  ### Expected Behavior
  
  ![image](https://user-images.githubusercontent.com/88175932/224484244-9e9653fe-2aa8-4f02-9bee-39942a2ab08f.png)
  
  
  <!--- Tell us what should happen -->
  
  ### Steps to Reproduce
  As shown above
  <!--- Provide a minimal example that reproduces the bug -->
  
  ### Environment
  
  <!--- Please provide details about your local environment -->
  
  Python version: 3.10.6
  NetworkX version: 3.0
  
  ### Additional context
  [https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.tree.operations.join.html](https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.tree.operations.join.html)
  
  <!--- Add any other context about the problem here, screenshots, etc. -->
  Improve test coverage for operations.py (join)
  <!-- If you have a general question about NetworkX, please use the discussions tab to create a new discussion -->
  
  <!--- Provide a general summary of the issue in the Title above -->
  
  ### Current Behavior
  https://app.codecov.io/gh/networkx/networkx/blob/main/networkx/algorithms/tree/operations.py  the current test coverage is 92.8%. There are still some cases needed to be handled.
  <!--- Tell us what happens instead of the expected behavior -->
  
  ### Expected Behavior
  
  <!--- Tell us what should happen -->
  https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.tree.operations.join.html
  1. Test case to check label_attribute should be added 
  2. In the documentation its written that the inputs must be tree. But this function works for graphs too. Could you tell me if its for  trees or graphs as well?
  ### Steps to Reproduce
  
  <!--- Provide a minimal example that reproduces the bug -->
  
  ### Environment
  
  <!--- Please provide details about your local environment -->
  
  Python version:3.10.6
  NetworkX version:3.0
  
  ### Additional context
  
  <!--- Add any other context about the problem here, screenshots, etc. -->
  
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `networkx/algorithms/tree/operations.py`
  Content:
  ```
  1 """Operations on trees."""
  2 from functools import partial
  3 from itertools import accumulate, chain
  4 
  5 import networkx as nx
  6 
  7 __all__ = ["join"]
  8 
  9 
  10 def join(rooted_trees, label_attribute=None):
  11     """Returns a new rooted tree with a root node joined with the roots
  12     of each of the given rooted trees.
  13 
  14     Parameters
  15     ----------
  16     rooted_trees : list
  17         A list of pairs in which each left element is a NetworkX graph
  18         object representing a tree and each right element is the root
  19         node of that tree. The nodes of these trees will be relabeled to
  20         integers.
  21 
  22     label_attribute : str
  23         If provided, the old node labels will be stored in the new tree
  24         under this node attribute. If not provided, the node attribute
  25         ``'_old'`` will store the original label of the node in the
  26         rooted trees given in the input.
  27 
  28     Returns
  29     -------
  30     NetworkX graph
  31         The rooted tree whose subtrees are the given rooted trees. The
  32         new root node is labeled 0. Each non-root node has an attribute,
  33         as described under the keyword argument ``label_attribute``,
  34         that indicates the label of the original node in the input tree.
  35 
  36     Notes
  37     -----
  38     Graph, edge, and node attributes are propagated from the given
  39     rooted trees to the created tree. If there are any overlapping graph
  40     attributes, those from later trees will overwrite those from earlier
  41     trees in the tuple of positional arguments.
  42 
  43     Examples
  44     --------
  45     Join two full balanced binary trees of height *h* to get a full
  46     balanced binary tree of depth *h* + 1::
  47 
  48         >>> h = 4
  49         >>> left = nx.balanced_tree(2, h)
  50         >>> right = nx.balanced_tree(2, h)
  51         >>> joined_tree = nx.join([(left, 0), (right, 0)])
  52         >>> nx.is_isomorphic(joined_tree, nx.balanced_tree(2, h + 1))
  53         True
  54 
  55     """
  56     if len(rooted_trees) == 0:
  57         return nx.empty_graph(1)
  58 
  59     # Unzip the zipped list of (tree, root) pairs.
  60     trees, roots = zip(*rooted_trees)
  61 
  62     # The join of the trees has the same type as the type of the first
  63     # tree.
  64     R = type(trees[0])()
  65 
  66     # Relabel the nodes so that their union is the integers starting at 1.
  67     if label_attribute is None:
  68         label_attribute = "_old"
  69     relabel = partial(
  70         nx.convert_node_labels_to_integers, label_attribute=label_attribute
  71     )
  72     lengths = (len(tree) for tree in trees[:-1])
  73     first_labels = chain([0], accumulate(lengths))
  74     trees = [
  75         relabel(tree, first_label=first_label + 1)
  76         for tree, first_label in zip(trees, first_labels)
  77     ]
  78 
  79     # Get the relabeled roots.
  80     roots = [
  81         next(v for v, d in tree.nodes(data=True) if d.get("_old") == root)
  82         for tree, root in zip(trees, roots)
  83     ]
  84 
  85     # Remove the old node labels.
  86     for tree in trees:
  87         for v in tree:
  88             tree.nodes[v].pop("_old")
  89 
  90     # Add all sets of nodes and edges, with data.
  91     nodes = (tree.nodes(data=True) for tree in trees)
  92     edges = (tree.edges(data=True) for tree in trees)
  93     R.add_nodes_from(chain.from_iterable(nodes))
  94     R.add_edges_from(chain.from_iterable(edges))
  95 
  96     # Add graph attributes; later attributes take precedent over earlier
  97     # attributes.
  98     for tree in trees:
  99         R.graph.update(tree.graph)
  100 
  101     # Finally, join the subtrees at the root. We know 0 is unused by the
  102     # way we relabeled the subtrees.
  103     R.add_node(0)
  104     R.add_edges_from((0, root) for root in roots)
  105 
  106     return R
  107
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/networkx/algorithms/tree/operations.py b/networkx/algorithms/tree/operations.py
  --- a/networkx/algorithms/tree/operations.py
  +++ b/networkx/algorithms/tree/operations.py
  @@ -78,25 +78,13 @@
   
       # Get the relabeled roots.
       roots = [
  -        next(v for v, d in tree.nodes(data=True) if d.get("_old") == root)
  +        next(v for v, d in tree.nodes(data=True) if d.get(label_attribute) == root)
           for tree, root in zip(trees, roots)
       ]
   
  -    # Remove the old node labels.
  +    # Add all sets of nodes and edges, attributes
       for tree in trees:
  -        for v in tree:
  -            tree.nodes[v].pop("_old")
  -
  -    # Add all sets of nodes and edges, with data.
  -    nodes = (tree.nodes(data=True) for tree in trees)
  -    edges = (tree.edges(data=True) for tree in trees)
  -    R.add_nodes_from(chain.from_iterable(nodes))
  -    R.add_edges_from(chain.from_iterable(edges))
  -
  -    # Add graph attributes; later attributes take precedent over earlier
  -    # attributes.
  -    for tree in trees:
  -        R.graph.update(tree.graph)
  +        R.update(tree)
   
       # Finally, join the subtrees at the root. We know 0 is unused by the
       # way we relabeled the subtrees.
  
verification_info: {"golden_diff": "diff --git a/networkx/algorithms/tree/operations.py b/networkx/algorithms/tree/operations.py\n--- a/networkx/algorithms/tree/operations.py\n+++ b/networkx/algorithms/tree/operations.py\n@@ -78,25 +78,13 @@\n \n     # Get the relabeled roots.\n     roots = [\n-        next(v for v, d in tree.nodes(data=True) if d.get(\"_old\") == root)\n+        next(v for v, d in tree.nodes(data=True) if d.get(label_attribute) == root)\n         for tree, root in zip(trees, roots)\n     ]\n \n-    # Remove the old node labels.\n+    # Add all sets of nodes and edges, attributes\n     for tree in trees:\n-        for v in tree:\n-            tree.nodes[v].pop(\"_old\")\n-\n-    # Add all sets of nodes and edges, with data.\n-    nodes = (tree.nodes(data=True) for tree in trees)\n-    edges = (tree.edges(data=True) for tree in trees)\n-    R.add_nodes_from(chain.from_iterable(nodes))\n-    R.add_edges_from(chain.from_iterable(edges))\n-\n-    # Add graph attributes; later attributes take precedent over earlier\n-    # attributes.\n-    for tree in trees:\n-        R.graph.update(tree.graph)\n+        R.update(tree)\n \n     # Finally, join the subtrees at the root. We know 0 is unused by the\n     # way we relabeled the subtrees.\n", "issue": "Join operation in trees---not handling label_attribute\n<!-- If you have a general question about NetworkX, please use the discussions tab to create a new discussion -->\r\n\r\n<!--- Provide a general summary of the issue in the Title above -->\r\n[https://github.com/networkx/networkx/blob/main/networkx/algorithms/tree/operations.py](https://github.com/networkx/networkx/blob/main/networkx/algorithms/tree/operations.py)\r\n1. The resulting graph of join operation in trees isn't including the old labels of inputs.\r\n2.  Not handling the cases where label_attribute is passed as an argument.\r\n\r\n### Current Behavior\r\n![Screenshot from 2023-03-11 17-03-33](https://user-images.githubusercontent.com/88175932/224483929-b1ebff93-2e5e-46a6-9c6e-11de1dc53ca1.png)\r\n\r\n<!--- Tell us what happens instead of the expected behavior -->\r\n\r\n### Expected Behavior\r\n\r\n![image](https://user-images.githubusercontent.com/88175932/224484244-9e9653fe-2aa8-4f02-9bee-39942a2ab08f.png)\r\n\r\n\r\n<!--- Tell us what should happen -->\r\n\r\n### Steps to Reproduce\r\nAs shown above\r\n<!--- Provide a minimal example that reproduces the bug -->\r\n\r\n### Environment\r\n\r\n<!--- Please provide details about your local environment -->\r\n\r\nPython version: 3.10.6\r\nNetworkX version: 3.0\r\n\r\n### Additional context\r\n[https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.tree.operations.join.html](https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.tree.operations.join.html)\r\n\r\n<!--- Add any other context about the problem here, screenshots, etc. -->\nImprove test coverage for operations.py (join)\n<!-- If you have a general question about NetworkX, please use the discussions tab to create a new discussion -->\r\n\r\n<!--- Provide a general summary of the issue in the Title above -->\r\n\r\n### Current Behavior\r\nhttps://app.codecov.io/gh/networkx/networkx/blob/main/networkx/algorithms/tree/operations.py  the current test coverage is 92.8%. There are still some cases needed to be handled.\r\n<!--- Tell us what happens instead of the expected behavior -->\r\n\r\n### Expected Behavior\r\n\r\n<!--- Tell us what should happen -->\r\nhttps://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.tree.operations.join.html\r\n1. Test case to check label_attribute should be added \r\n2. In the documentation its written that the inputs must be tree. But this function works for graphs too. Could you tell me if its for  trees or graphs as well?\r\n### Steps to Reproduce\r\n\r\n<!--- Provide a minimal example that reproduces the bug -->\r\n\r\n### Environment\r\n\r\n<!--- Please provide details about your local environment -->\r\n\r\nPython version:3.10.6\r\nNetworkX version:3.0\r\n\r\n### Additional context\r\n\r\n<!--- Add any other context about the problem here, screenshots, etc. -->\r\n\n", "before_files": [{"content": "\"\"\"Operations on trees.\"\"\"\nfrom functools import partial\nfrom itertools import accumulate, chain\n\nimport networkx as nx\n\n__all__ = [\"join\"]\n\n\ndef join(rooted_trees, label_attribute=None):\n    \"\"\"Returns a new rooted tree with a root node joined with the roots\n    of each of the given rooted trees.\n\n    Parameters\n    ----------\n    rooted_trees : list\n        A list of pairs in which each left element is a NetworkX graph\n        object representing a tree and each right element is the root\n        node of that tree. The nodes of these trees will be relabeled to\n        integers.\n\n    label_attribute : str\n        If provided, the old node labels will be stored in the new tree\n        under this node attribute. If not provided, the node attribute\n        ``'_old'`` will store the original label of the node in the\n        rooted trees given in the input.\n\n    Returns\n    -------\n    NetworkX graph\n        The rooted tree whose subtrees are the given rooted trees. The\n        new root node is labeled 0. Each non-root node has an attribute,\n        as described under the keyword argument ``label_attribute``,\n        that indicates the label of the original node in the input tree.\n\n    Notes\n    -----\n    Graph, edge, and node attributes are propagated from the given\n    rooted trees to the created tree. If there are any overlapping graph\n    attributes, those from later trees will overwrite those from earlier\n    trees in the tuple of positional arguments.\n\n    Examples\n    --------\n    Join two full balanced binary trees of height *h* to get a full\n    balanced binary tree of depth *h* + 1::\n\n        >>> h = 4\n        >>> left = nx.balanced_tree(2, h)\n        >>> right = nx.balanced_tree(2, h)\n        >>> joined_tree = nx.join([(left, 0), (right, 0)])\n        >>> nx.is_isomorphic(joined_tree, nx.balanced_tree(2, h + 1))\n        True\n\n    \"\"\"\n    if len(rooted_trees) == 0:\n        return nx.empty_graph(1)\n\n    # Unzip the zipped list of (tree, root) pairs.\n    trees, roots = zip(*rooted_trees)\n\n    # The join of the trees has the same type as the type of the first\n    # tree.\n    R = type(trees[0])()\n\n    # Relabel the nodes so that their union is the integers starting at 1.\n    if label_attribute is None:\n        label_attribute = \"_old\"\n    relabel = partial(\n        nx.convert_node_labels_to_integers, label_attribute=label_attribute\n    )\n    lengths = (len(tree) for tree in trees[:-1])\n    first_labels = chain([0], accumulate(lengths))\n    trees = [\n        relabel(tree, first_label=first_label + 1)\n        for tree, first_label in zip(trees, first_labels)\n    ]\n\n    # Get the relabeled roots.\n    roots = [\n        next(v for v, d in tree.nodes(data=True) if d.get(\"_old\") == root)\n        for tree, root in zip(trees, roots)\n    ]\n\n    # Remove the old node labels.\n    for tree in trees:\n        for v in tree:\n            tree.nodes[v].pop(\"_old\")\n\n    # Add all sets of nodes and edges, with data.\n    nodes = (tree.nodes(data=True) for tree in trees)\n    edges = (tree.edges(data=True) for tree in trees)\n    R.add_nodes_from(chain.from_iterable(nodes))\n    R.add_edges_from(chain.from_iterable(edges))\n\n    # Add graph attributes; later attributes take precedent over earlier\n    # attributes.\n    for tree in trees:\n        R.graph.update(tree.graph)\n\n    # Finally, join the subtrees at the root. We know 0 is unused by the\n    # way we relabeled the subtrees.\n    R.add_node(0)\n    R.add_edges_from((0, root) for root in roots)\n\n    return R\n", "path": "networkx/algorithms/tree/operations.py"}], "after_files": [{"content": "\"\"\"Operations on trees.\"\"\"\nfrom functools import partial\nfrom itertools import accumulate, chain\n\nimport networkx as nx\n\n__all__ = [\"join\"]\n\n\ndef join(rooted_trees, label_attribute=None):\n    \"\"\"Returns a new rooted tree with a root node joined with the roots\n    of each of the given rooted trees.\n\n    Parameters\n    ----------\n    rooted_trees : list\n        A list of pairs in which each left element is a NetworkX graph\n        object representing a tree and each right element is the root\n        node of that tree. The nodes of these trees will be relabeled to\n        integers.\n\n    label_attribute : str\n        If provided, the old node labels will be stored in the new tree\n        under this node attribute. If not provided, the node attribute\n        ``'_old'`` will store the original label of the node in the\n        rooted trees given in the input.\n\n    Returns\n    -------\n    NetworkX graph\n        The rooted tree whose subtrees are the given rooted trees. The\n        new root node is labeled 0. Each non-root node has an attribute,\n        as described under the keyword argument ``label_attribute``,\n        that indicates the label of the original node in the input tree.\n\n    Notes\n    -----\n    Graph, edge, and node attributes are propagated from the given\n    rooted trees to the created tree. If there are any overlapping graph\n    attributes, those from later trees will overwrite those from earlier\n    trees in the tuple of positional arguments.\n\n    Examples\n    --------\n    Join two full balanced binary trees of height *h* to get a full\n    balanced binary tree of depth *h* + 1::\n\n        >>> h = 4\n        >>> left = nx.balanced_tree(2, h)\n        >>> right = nx.balanced_tree(2, h)\n        >>> joined_tree = nx.join([(left, 0), (right, 0)])\n        >>> nx.is_isomorphic(joined_tree, nx.balanced_tree(2, h + 1))\n        True\n\n    \"\"\"\n    if len(rooted_trees) == 0:\n        return nx.empty_graph(1)\n\n    # Unzip the zipped list of (tree, root) pairs.\n    trees, roots = zip(*rooted_trees)\n\n    # The join of the trees has the same type as the type of the first\n    # tree.\n    R = type(trees[0])()\n\n    # Relabel the nodes so that their union is the integers starting at 1.\n    if label_attribute is None:\n        label_attribute = \"_old\"\n    relabel = partial(\n        nx.convert_node_labels_to_integers, label_attribute=label_attribute\n    )\n    lengths = (len(tree) for tree in trees[:-1])\n    first_labels = chain([0], accumulate(lengths))\n    trees = [\n        relabel(tree, first_label=first_label + 1)\n        for tree, first_label in zip(trees, first_labels)\n    ]\n\n    # Get the relabeled roots.\n    roots = [\n        next(v for v, d in tree.nodes(data=True) if d.get(label_attribute) == root)\n        for tree, root in zip(trees, roots)\n    ]\n\n    # Add all sets of nodes and edges, attributes\n    for tree in trees:\n        R.update(tree)\n\n    # Finally, join the subtrees at the root. We know 0 is unused by the\n    # way we relabeled the subtrees.\n    R.add_node(0)\n    R.add_edges_from((0, root) for root in roots)\n\n    return R\n", "path": "networkx/algorithms/tree/operations.py"}]}