---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-27-68727e4bbc1e> in <module>
      4 var = pd.DataFrame(index=['gene1', 'gene2', 'gene2'])
      5 test = an.AnnData(X=x, obs=obs, var=var)
----> 6 an.concat((test, test))

~/miniconda3/envs/dev/lib/python3.8/site-packages/anndata/_core/merge.py in concat(adatas, axis, join, merge, uns_merge, label, keys, index_unique, fill_value, pairwise)
    812 
    813     # Annotation for other axis
--> 814     alt_annot = merge_dataframes(
    815         [getattr(a, alt_dim) for a in adatas], alt_indices, merge
    816     )

~/miniconda3/envs/dev/lib/python3.8/site-packages/anndata/_core/merge.py in merge_dataframes(dfs, new_index, merge_strategy)
    524 
    525 def merge_dataframes(dfs, new_index, merge_strategy=merge_unique):
--> 526     dfs = [df.reindex(index=new_index) for df in dfs]
    527     # New dataframe with all shared data
    528     new_df = pd.DataFrame(merge_strategy(dfs), index=new_index)

~/miniconda3/envs/dev/lib/python3.8/site-packages/anndata/_core/merge.py in <listcomp>(.0)
    524 
    525 def merge_dataframes(dfs, new_index, merge_strategy=merge_unique):
--> 526     dfs = [df.reindex(index=new_index) for df in dfs]
    527     # New dataframe with all shared data
    528     new_df = pd.DataFrame(merge_strategy(dfs), index=new_index)

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/util/_decorators.py in wrapper(*args, **kwargs)
    310         @wraps(func)
    311         def wrapper(*args, **kwargs) -> Callable[..., Any]:
--> 312             return func(*args, **kwargs)
    313 
    314         kind = inspect.Parameter.POSITIONAL_OR_KEYWORD

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/frame.py in reindex(self, *args, **kwargs)
   4171         kwargs.pop("axis", None)
   4172         kwargs.pop("labels", None)
-> 4173         return super().reindex(**kwargs)
   4174 
   4175     def drop(

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/generic.py in reindex(self, *args, **kwargs)
   4804 
   4805         # perform the reindex on the axes
-> 4806         return self._reindex_axes(
   4807             axes, level, limit, tolerance, method, fill_value, copy
   4808         ).__finalize__(self, method="reindex")

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/frame.py in _reindex_axes(self, axes, level, limit, tolerance, method, fill_value, copy)
   4017         index = axes["index"]
   4018         if index is not None:
-> 4019             frame = frame._reindex_index(
   4020                 index, method, copy, level, fill_value, limit, tolerance
   4021             )

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/frame.py in _reindex_index(self, new_index, method, copy, level, fill_value, limit, tolerance)
   4036             new_index, method=method, level=level, limit=limit, tolerance=tolerance
   4037         )
-> 4038         return self._reindex_with_indexers(
   4039             {0: [new_index, indexer]},
   4040             copy=copy,

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/generic.py in _reindex_with_indexers(self, reindexers, fill_value, copy, allow_dups)
   4870 
   4871             # TODO: speed up on homogeneous DataFrame objects
-> 4872             new_data = new_data.reindex_indexer(
   4873                 index,
   4874                 indexer,

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/internals/managers.py in reindex_indexer(self, new_axis, indexer, axis, fill_value, allow_dups, copy, consolidate, only_slice)
   1299         # some axes don't allow reindexing with dups
   1300         if not allow_dups:
-> 1301             self.axes[axis]._can_reindex(indexer)
   1302 
   1303         if axis >= self.ndim:

~/miniconda3/envs/dev/lib/python3.8/site-packages/pandas/core/indexes/base.py in _can_reindex(self, indexer)
   3474         # trying to reindex on an axis with duplicates
   3475         if not self._index_as_unique and len(indexer):
-> 3476             raise ValueError("cannot reindex from a duplicate axis")
   3477 
   3478     def reindex(self, target, method=None, level=None, limit=None, tolerance=None):

ValueError: cannot reindex from a duplicate axis