What happened?

I make a dataset with some variables, and make them all coordinates. Then I try to query on the dataset. Error ensues.

What did you expect to happen?

No error.

Minimal Complete Verifiable Example

```Python import xarray as xr import pandas as pd x = xr.Dataset.from_dataframe(pd.DataFrame(data=[[0,1],[2,3]],columns=['a','b']))

display(x.query(index='a==0')) #fine

y = x.set_coords(['a','b'])

display(y) #fine

y.query(index='a==0') #error ```

Relevant log output

```Python

KeyError Traceback (most recent call last) ~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/scope.py in resolve(self, key, is_local) 199 assert not is_local and not self.has_resolvers --> 200 return self.scope[key] 201 except KeyError:

~/miniconda3/lib/python3.9/collections/init.py in getitem(self, key) 940 pass --> 941 return self.missing(key) # support subclasses that define missing 942

~/miniconda3/lib/python3.9/collections/init.py in missing(self, key) 932 def missing(self, key): --> 933 raise KeyError(key) 934

KeyError: 'a'

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last) ~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/scope.py in resolve(self, key, is_local) 205 # e.g., df[df > 0] --> 206 return self.temps[key] 207 except KeyError as err:

KeyError: 'a'

The above exception was the direct cause of the following exception:

UndefinedVariableError Traceback (most recent call last) /tmp/ipykernel_23733/4091370488.py in <cell line: 7>() 5 y = x.set_coords(['a','b']) 6 display(y) ----> 7 y.query(index='a==0')

~/miniconda3/lib/python3.9/site-packages/xarray/core/dataset.py in query(self, queries, parser, engine, missing_dims, **queries_kwargs) 7605 7606 # evaluate the queries to create the indexers -> 7607 indexers = { 7608 dim: pd.eval(expr, resolvers=[self], parser=parser, engine=engine) 7609 for dim, expr in queries.items()

~/miniconda3/lib/python3.9/site-packages/xarray/core/dataset.py in <dictcomp>(.0) 7606 # evaluate the queries to create the indexers 7607 indexers = { -> 7608 dim: pd.eval(expr, resolvers=[self], parser=parser, engine=engine) 7609 for dim, expr in queries.items() 7610 }

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/eval.py in eval(expr, parser, engine, truediv, local_dict, global_dict, resolvers, level, target, inplace) 348 ) 349 --> 350 parsed_expr = Expr(expr, engine=engine, parser=parser, env=env) 351 352 # construct the engine and evaluate the parsed expression

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in init(self, expr, engine, parser, env, level) 809 self.parser = parser 810 self._visitor = PARSERSparser --> 811 self.terms = self.parse() 812 813 @property

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in parse(self) 828 Parse an expression. 829 """ --> 830 return self._visitor.visit(self.expr) 831 832 @property

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Module(self, node, kwargs) 419 raise SyntaxError("only a single expression is allowed") 420 expr = node.body[0] --> 421 return self.visit(expr, kwargs) 422 423 def visit_Expr(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Expr(self, node, kwargs) 422 423 def visit_Expr(self, node, kwargs): --> 424 return self.visit(node.value, **kwargs) 425 426 def _rewrite_membership_op(self, node, left, right):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Compare(self, node, **kwargs) 721 op = self.translate_In(ops[0]) 722 binop = ast.BinOp(op=op, left=node.left, right=comps[0]) --> 723 return self.visit(binop) 724 725 # recursive case: we have a chained comparison, a CMP b CMP c, etc.

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_BinOp(self, node, kwargs) 534 535 def visit_BinOp(self, node, kwargs): --> 536 op, op_class, left, right = self._maybe_transform_eq_ne(node) 537 left, right = self._maybe_downcast_constants(left, right) 538 return self._maybe_evaluate_binop(op, op_class, left, right)

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in _maybe_transform_eq_ne(self, node, left, right) 454 def _maybe_transform_eq_ne(self, node, left=None, right=None): 455 if left is None: --> 456 left = self.visit(node.left, side="left") 457 if right is None: 458 right = self.visit(node.right, side="right")

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit(self, node, kwargs) 413 method = "visit_" + type(node).name 414 visitor = getattr(self, method) --> 415 return visitor(node, kwargs) 416 417 def visit_Module(self, node, **kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/expr.py in visit_Name(self, node, kwargs) 547 548 def visit_Name(self, node, kwargs): --> 549 return self.term_type(node.id, self.env, kwargs) 550 551 def visit_NameConstant(self, node, kwargs):

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/ops.py in init(self, name, env, side, encoding) 96 tname = str(name) 97 self.is_local = tname.startswith(LOCAL_TAG) or tname in DEFAULT_GLOBALS ---> 98 self._value = self._resolve_name() 99 self.encoding = encoding 100

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/ops.py in _resolve_name(self) 113 114 def _resolve_name(self): --> 115 res = self.env.resolve(self.local_name, is_local=self.is_local) 116 self.update(res) 117

~/miniconda3/lib/python3.9/site-packages/pandas/core/computation/scope.py in resolve(self, key, is_local) 209 from pandas.core.computation.ops import UndefinedVariableError 210 --> 211 raise UndefinedVariableError(key, is_local) from err 212 213 def swapkey(self, old_key: str, new_key: str, new_value=None) -> None:

UndefinedVariableError: name 'a' is not defined ```

Anything else we need to know?

If the dataset has one data variable, then the error does not happen.

Environment

INSTALLED VERSIONS

commit: None python: 3.9.12 | packaged by conda-forge | (main, Mar 24 2022, 23:25:59) [GCC 10.3.0] python-bits: 64 OS: Linux OS-release: 4.19.0-19-amd64 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.12.1 libnetcdf: 4.8.1

xarray: 2022.3.0 pandas: 1.4.1 numpy: 1.22.3 scipy: 1.8.0 netCDF4: 1.5.8 pydap: None h5netcdf: 1.0.0 h5py: 3.6.0 Nio: None zarr: 2.11.1 cftime: 1.5.2 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2022.03.0 distributed: 2022.3.0 matplotlib: 3.5.1 cartopy: None seaborn: 0.11.2 numbagg: None fsspec: 2022.02.0 cupy: None pint: 0.18 sparse: 0.13.0 setuptools: 59.8.0 pip: 22.0.4 conda: 4.12.0 pytest: 7.1.1 IPython: 7.32.0 sphinx: None