prompt: You will be provided with a partial code base and an issue statement explaining a problem to resolve.
  <issue>
  bug: isolated dask backend tests fail due to removed imports
  For some reason lines 6 and 8 here: https://github.com/ibis-project/ibis/commit/a1262410310bb4d638a73e1cdfbe93c2b4089905#diff-96d84d9b6e9e84a2be7a046dc9853df1ca5fc6e894307339b02cd61e666c0149L6-L8
  
  were removed.
  
  This causes dasks tests to fail when they are run in isolation from other tests that (transitively) import from the pandas backend.
  
  This is both a ci bug and a bug in the code, since we're not testing backends independently. Perhaps unsurprisingly I discovered the bug in #2937, which fixes the CI part of this problem.
  
  </issue>
  <code>
  [start of ibis/backends/dask/__init__.py]
  1 from typing import Mapping
  2 
  3 import dask
  4 import dask.dataframe as dd
  5 import pandas as pd
  6 import toolz
  7 from dask.base import DaskMethodsMixin
  8 
  9 import ibis.common.exceptions as com
  10 import ibis.config
  11 import ibis.expr.schema as sch
  12 import ibis.expr.types as ir
  13 from ibis.backends.pandas import BasePandasBackend
  14 
  15 from .client import DaskDatabase, DaskTable, ibis_schema_to_dask
  16 from .core import execute_and_reset
  17 
  18 # Make sure that the pandas backend is loaded, dispatching has been
  19 # executed, and options have been loaded
  20 ibis.pandas
  21 
  22 
  23 class Backend(BasePandasBackend):
  24     name = 'dask'
  25     database_class = DaskDatabase
  26     table_class = DaskTable
  27 
  28     def connect(self, dictionary):
  29         # register dispatchers
  30         from . import udf  # noqa: F401
  31 
  32         return super().connect(dictionary)
  33 
  34     @property
  35     def version(self):
  36         return dask.__version__
  37 
  38     def execute(
  39         self,
  40         query: ir.Expr,
  41         params: Mapping[ir.Expr, object] = None,
  42         limit: str = 'default',
  43         **kwargs,
  44     ):
  45         if limit != 'default':
  46             raise ValueError(
  47                 'limit parameter to execute is not yet implemented in the '
  48                 'dask backend'
  49             )
  50 
  51         if not isinstance(query, ir.Expr):
  52             raise TypeError(
  53                 "`query` has type {!r}, expected ibis.expr.types.Expr".format(
  54                     type(query).__name__
  55                 )
  56             )
  57 
  58         result = self.compile(query, params, **kwargs)
  59         if isinstance(result, DaskMethodsMixin):
  60             return result.compute()
  61         else:
  62             return result
  63 
  64     def compile(
  65         self, query: ir.Expr, params: Mapping[ir.Expr, object] = None, **kwargs
  66     ):
  67         """Compile `expr`.
  68 
  69         Notes
  70         -----
  71         For the dask backend returns a dask graph that you can run ``.compute``
  72         on to get a pandas object.
  73 
  74         """
  75         return execute_and_reset(query, params=params, **kwargs)
  76 
  77     def create_table(
  78         self,
  79         table_name: str,
  80         obj: dd.DataFrame = None,
  81         schema: sch.Schema = None,
  82     ):
  83         """Create a table."""
  84         if obj is not None:
  85             df = obj
  86         elif schema is not None:
  87             dtypes = ibis_schema_to_dask(schema)
  88             df = schema.apply_to(
  89                 dd.from_pandas(
  90                     pd.DataFrame(columns=list(map(toolz.first, dtypes))),
  91                     npartitions=1,
  92                 )
  93             )
  94         else:
  95             raise com.IbisError('Must pass expr or schema')
  96 
  97         self.dictionary[table_name] = df
  98
  [end of ibis/backends/dask/__init__.py]
  </code>
  
  I need you to solve this issue by generating a single patch file that I can apply directly to this repository using git apply. Please respond with a single patch file in the following format.
  <patch>
  diff --git a/file.py b/file.py
  --- a/file.py
  +++ b/file.py
  @@ -1,27 +1,35 @@
   def euclidean(a, b):
  -    while b:
  -        a, b = b, a % b
  -    return a
  +    if b == 0:
  +        return a
  +    return euclidean(b, a % b)
   
   
   def bresenham(x0, y0, x1, y1):
       points = []
       dx = abs(x1 - x0)
       dy = abs(y1 - y0)
  -    sx = 1 if x0 < x1 else -1
  -    sy = 1 if y0 < y1 else -1
  -    err = dx - dy
  +    x, y = x0, y0
  +    sx = -1 if x0 > x1 else 1
  +    sy = -1 if y0 > y1 else 1
   
  -    while True:
  -        points.append((x0, y0))
  -        if x0 == x1 and y0 == y1:
  -            break
  -        e2 = 2 * err
  -        if e2 > -dy:
  -            err -= dy
  -            x0 += sx
  -        if e2 < dx:
  -            err += dx
  -            y0 += sy
  +    if dx > dy:
  +        err = dx / 2.0
  +        while x != x1:
  +            points.append((x, y))
  +            err -= dy
  +            if err < 0:
  +                y += sy
  +                err += dx
  +            x += sx
  +    else:
  +        err = dy / 2.0
  +        while y != y1:
  +            points.append((x, y))
  +            err -= dx
  +            if err < 0:
  +                x += sx
  +                err += dy
  +            y += sy
  +
  +    points.append((x, y))
       return points
  
  </patch>
golden_diff: diff --git a/ibis/backends/dask/__init__.py b/ibis/backends/dask/__init__.py
  --- a/ibis/backends/dask/__init__.py
  +++ b/ibis/backends/dask/__init__.py
  @@ -6,6 +6,9 @@
   import toolz
   from dask.base import DaskMethodsMixin
   
  +# import the pandas execution module to register dispatched implementations of
  +# execute_node that the dask backend will later override
  +import ibis.backends.pandas.execution  # noqa: F401
   import ibis.common.exceptions as com
   import ibis.config
   import ibis.expr.schema as sch
  @@ -15,8 +18,7 @@
   from .client import DaskDatabase, DaskTable, ibis_schema_to_dask
   from .core import execute_and_reset
   
  -# Make sure that the pandas backend is loaded, dispatching has been
  -# executed, and options have been loaded
  +# Make sure that the pandas backend options have been loaded
   ibis.pandas
  
verification_info: {"golden_diff": "diff --git a/ibis/backends/dask/__init__.py b/ibis/backends/dask/__init__.py\n--- a/ibis/backends/dask/__init__.py\n+++ b/ibis/backends/dask/__init__.py\n@@ -6,6 +6,9 @@\n import toolz\n from dask.base import DaskMethodsMixin\n \n+# import the pandas execution module to register dispatched implementations of\n+# execute_node that the dask backend will later override\n+import ibis.backends.pandas.execution  # noqa: F401\n import ibis.common.exceptions as com\n import ibis.config\n import ibis.expr.schema as sch\n@@ -15,8 +18,7 @@\n from .client import DaskDatabase, DaskTable, ibis_schema_to_dask\n from .core import execute_and_reset\n \n-# Make sure that the pandas backend is loaded, dispatching has been\n-# executed, and options have been loaded\n+# Make sure that the pandas backend options have been loaded\n ibis.pandas\n", "issue": "bug: isolated dask backend tests fail due to removed imports\nFor some reason lines 6 and 8 here: https://github.com/ibis-project/ibis/commit/a1262410310bb4d638a73e1cdfbe93c2b4089905#diff-96d84d9b6e9e84a2be7a046dc9853df1ca5fc6e894307339b02cd61e666c0149L6-L8\r\n\r\nwere removed.\r\n\r\nThis causes dasks tests to fail when they are run in isolation from other tests that (transitively) import from the pandas backend.\r\n\r\nThis is both a ci bug and a bug in the code, since we're not testing backends independently. Perhaps unsurprisingly I discovered the bug in #2937, which fixes the CI part of this problem.\n", "before_files": [{"content": "from typing import Mapping\n\nimport dask\nimport dask.dataframe as dd\nimport pandas as pd\nimport toolz\nfrom dask.base import DaskMethodsMixin\n\nimport ibis.common.exceptions as com\nimport ibis.config\nimport ibis.expr.schema as sch\nimport ibis.expr.types as ir\nfrom ibis.backends.pandas import BasePandasBackend\n\nfrom .client import DaskDatabase, DaskTable, ibis_schema_to_dask\nfrom .core import execute_and_reset\n\n# Make sure that the pandas backend is loaded, dispatching has been\n# executed, and options have been loaded\nibis.pandas\n\n\nclass Backend(BasePandasBackend):\n    name = 'dask'\n    database_class = DaskDatabase\n    table_class = DaskTable\n\n    def connect(self, dictionary):\n        # register dispatchers\n        from . import udf  # noqa: F401\n\n        return super().connect(dictionary)\n\n    @property\n    def version(self):\n        return dask.__version__\n\n    def execute(\n        self,\n        query: ir.Expr,\n        params: Mapping[ir.Expr, object] = None,\n        limit: str = 'default',\n        **kwargs,\n    ):\n        if limit != 'default':\n            raise ValueError(\n                'limit parameter to execute is not yet implemented in the '\n                'dask backend'\n            )\n\n        if not isinstance(query, ir.Expr):\n            raise TypeError(\n                \"`query` has type {!r}, expected ibis.expr.types.Expr\".format(\n                    type(query).__name__\n                )\n            )\n\n        result = self.compile(query, params, **kwargs)\n        if isinstance(result, DaskMethodsMixin):\n            return result.compute()\n        else:\n            return result\n\n    def compile(\n        self, query: ir.Expr, params: Mapping[ir.Expr, object] = None, **kwargs\n    ):\n        \"\"\"Compile `expr`.\n\n        Notes\n        -----\n        For the dask backend returns a dask graph that you can run ``.compute``\n        on to get a pandas object.\n\n        \"\"\"\n        return execute_and_reset(query, params=params, **kwargs)\n\n    def create_table(\n        self,\n        table_name: str,\n        obj: dd.DataFrame = None,\n        schema: sch.Schema = None,\n    ):\n        \"\"\"Create a table.\"\"\"\n        if obj is not None:\n            df = obj\n        elif schema is not None:\n            dtypes = ibis_schema_to_dask(schema)\n            df = schema.apply_to(\n                dd.from_pandas(\n                    pd.DataFrame(columns=list(map(toolz.first, dtypes))),\n                    npartitions=1,\n                )\n            )\n        else:\n            raise com.IbisError('Must pass expr or schema')\n\n        self.dictionary[table_name] = df\n", "path": "ibis/backends/dask/__init__.py"}]}