Lazy load dask.dataframe in datashader.py (#6309)

Co-authored-by: Maxime Liquet <[email protected]>

holoviews/core/util.py

@@ -1,6 +1,8 @@
 import builtins
 import datetime as dt
+import functools
 import hashlib
+import importlib
 import inspect
 import itertools
 import json
@@ -2331,3 +2333,30 @@ def flatten(line):
             yield from flatten(element)
         else:
             yield element
+
+
+def lazy_isinstance(obj, class_or_tuple):
+    """ Lazy isinstance check
+
+    Will only import the module of the object if the module of the
+    obj matches the first value of an item in class_or_tuple.
+
+    lazy_isinstance(obj, 'dask.dataframe:DataFrame')
+
+    Will:
+        1) check if the first module is dask
+        2) If it dask, import dask.dataframe
+        3) Do an isinstance check for dask.dataframe.DataFrame
+    """
+    if isinstance(class_or_tuple, str):
+        class_or_tuple = (class_or_tuple,)
+
+    obj_mod_name = obj.__module__.split('.')[0]
+    for cls in class_or_tuple:
+        mod_name, _, attr_name = cls.partition(':')
+        if not obj_mod_name.startswith(mod_name.split(".")[0]):
+            continue
+        mod = importlib.import_module(mod_name)
+        if isinstance(obj, functools.reduce(getattr, attr_name.split('.'), mod)):
+            return True
+    return False

holoviews/operation/datashader.py

@@ -2,7 +2,6 @@
 from collections.abc import Callable, Iterable
 from functools import partial
 
-import dask.dataframe as dd
 import datashader as ds
 import datashader.reductions as rd
 import datashader.transfer_functions as tf
@@ -45,6 +44,7 @@
     datetime_types,
     dt_to_int,
     get_param_values,
+    lazy_isinstance,
 )
 from ..element import (
     RGB,
@@ -303,22 +303,23 @@ def get_agg_data(cls, obj, category=None):
         if len(paths) > 1:
             if glyph == 'line':
                 path = paths[0][:1]
-                if isinstance(path, dd.DataFrame):
+                if lazy_isinstance(path, "dask.dataframe:DataFrame"):
                     path = path.compute()
                 empty = path.copy()
                 empty.iloc[0, :] = (np.nan,) * empty.shape[1]
                 paths = [elem for p in paths for elem in (p, empty)][:-1]
-            if all(isinstance(path, dd.DataFrame) for path in paths):
+            if all(lazy_isinstance(path,"dask.dataframe:DataFrame") for path in paths):
+                import dask.dataframe as dd
                 df = dd.concat(paths)
             else:
-                paths = [p.compute() if isinstance(p, dd.DataFrame) else p for p in paths]
+                paths = [p.compute() if lazy_isinstance(p, "dask.dataframe:DataFrame") else p for p in paths]
                 df = pd.concat(paths)
         else:
             df = paths[0] if paths else pd.DataFrame([], columns=[x.name, y.name])
         if category and df[category].dtype.name != 'category':
             df[category] = df[category].astype('category')
 
-        is_custom = isinstance(df, dd.DataFrame) or cuDFInterface.applies(df)
+        is_custom = lazy_isinstance(df, "dask.dataframe:DataFrame") or cuDFInterface.applies(df)
         if any((not is_custom and len(df[d.name]) and isinstance(df[d.name].values[0], cftime_types)) or
                df[d.name].dtype.kind in ["M", "u"] for d in (x, y)):
             df = df.copy()