dask: Data collapse methods and functions

cf/__init__.py

@@ -78,7 +78,7 @@
 __date__ = "2022-01-18"
 __version__ = "4.0.0b0"
 
-_requires = ("numpy", "netCDF4", "cftime", "cfunits", "cfdm", "psutil")
+_requires = ("numpy", "netCDF4", "cftime", "cfunits", "cfdm", "psutil", "dask")
 
 x = ", ".join(_requires)
 _error0 = f"cf v{ __version__} requires the modules {x}. "
@@ -104,10 +104,6 @@
 
 _found_ESMF = bool(importlib.util.find_spec("ESMF"))
 
-# TODODASK - Remove the next 2 lines when the move to dask is complete
-mpi_on = False
-mpi_size = 1
-
 try:
     import netCDF4
 except ImportError as error1:
@@ -133,6 +129,11 @@
 except ImportError as error1:
     raise ImportError(_error0 + str(error1))
 
+try:
+    import dask
+except ImportError as error1:
+    raise ImportError(_error0 + str(error1))
+
 # Check the version of psutil
 _minimum_vn = "0.6.0"
 if LooseVersion(psutil.__version__) < LooseVersion(_minimum_vn):
@@ -183,6 +184,14 @@
         f"Got {_cfdm_version} at {cfdm.__file__}"
     )
 
+# Check the version of dask
+_minimum_vn = "2022.03.0"
+if LooseVersion(dask.__version__) < LooseVersion(_minimum_vn):
+    raise RuntimeError(
+        f"Bad dask version: cf requires dask>={_minimum_vn}. "
+        f"Got {dask.__version__} at {dask.__file__}"
+    )
+
 from .constructs import Constructs
 
 from .mixin import Coordinate