Handles import with exception (#539)

* handles import with exception

* Remove debris from previous change

* reformat with black

python/mspasspy/db/database.py

@@ -14,23 +14,12 @@
 import fcntl
 
 try:
-    import dask.bag as daskbag
+    import dask.dataframe as daskdf
 
     _mspasspy_has_dask = True
 except ImportError:
     _mspasspy_has_dask = False
 
-try:
-    import dask.dataframe as daskdf
-except ImportError:
-    _mspasspy_has_dask = False
-
-try:
-    import pyspark
-
-    _mspasspy_has_pyspark = True
-except ImportError:
-    _mspasspy_has_pyspark = False
 
 import gridfs
 import pymongo
@@ -5864,7 +5853,7 @@ def save_dataframe(
         """
         dbcol = self[collection]
 
-        if parallel:
+        if parallel and _mspasspy_has_dask:
             df = daskdf.from_pandas(df, chunksize=1, sort=False)
 
         if not one_to_one:
@@ -5880,7 +5869,7 @@ def save_dataframe(
                     df[key] = df[key].mask(df[key] == val, None)
 
         """
-        if parallel:
+        if parallel and _mspasspy_has_dask:
             df = daskdf.from_pandas(df, chunksize=1, sort=False)
             df = df.apply(lambda x: x.dropna(), axis=1).compute()
         else:

python/mspasspy/io/distributed.py

@@ -22,8 +22,24 @@
     ErrorLogger,
 )
 
-import dask
-import pyspark
+try:
+    import dask
+
+    _mspasspy_has_dask = True
+except ImportError:
+    _mspasspy_has_dask = False
+try:
+    import pyspark
+
+    _mspasspy_has_pyspark = True
+except ImportError:
+    _mspasspy_has_pyspark = False
+
+if not _mspasspy_has_dask and not _mspasspy_has_pyspark:
+    message = "{} requires either dask or pyspark module. Please install dask or pyspark".format(
+        __name__
+    )
+    raise ModuleNotFoundError(message)
 
 
 def read_ensemble_parallel(
@@ -460,6 +476,11 @@ def read_distributed_data(
         message += "Unsupported value for scheduler={}\n".format(scheduler)
         message += "Must be either 'dask' or 'spark'"
         raise ValueError(message)
+    if scheduler == "spark" and not _mspasspy_has_pyspark:
+        print(
+            "WARNING(read_distributed_data): pyspark not found, will use dask instead. The scheduler argument is ignored."
+        )
+        scheduler = "dask"
 
     if isinstance(data, list):
         ensemble_mode = True
@@ -491,9 +512,10 @@ def read_distributed_data(
         ensemble_mode = False
         dataframe_input = False
         db = data
-    elif isinstance(
-        data,
-        (pd.DataFrame, pyspark.sql.dataframe.DataFrame, dask.dataframe.core.DataFrame),
+    elif (
+        isinstance(data, pd.DataFrame)
+        or (_mspasspy_has_dask and isinstance(data, dask.dataframe.core.DataFrame))
+        or (_mspasspy_has_pyspark and isinstance(data, pyspark.sql.dataframe.DataFrame))
     ):
         ensemble_mode = False
         dataframe_input = True
@@ -539,7 +561,6 @@ def read_distributed_data(
                 )
                 raise TypeError(message)
             container_partitions = container_to_merge.getNumPartitions()
-
         else:
             if not isinstance(container_to_merge, dask.bag.core.Bag):
                 message += (
@@ -1512,6 +1533,11 @@ class method `save_data`.  See the docstring for details but the
             )
             message += "Must be either dask or spark"
             raise ValueError(message)
+        if scheduler == "spark" and not _mspasspy_has_pyspark:
+            print(
+                "WARNING(write_distributed_data): pyspark not found, will use dask instead. The scheduler argument is ignored."
+            )
+            scheduler = "dask"
     else:
         scheduler = "dask"
     # This use of the collection name to establish the schema is