Update client.py to be consistent with the docstring (#7705)

distributed/client.py

@@ -1839,7 +1839,7 @@ def submit(
         allow_other_workers=False,
         actor=False,
         actors=False,
-        pure=None,
+        pure=True,
         **kwargs,
     ):
         """Submit a function application to the scheduler
@@ -1880,7 +1880,9 @@ def submit(
             Alias for `actor`
         pure : bool (defaults to True)
             Whether or not the function is pure.  Set ``pure=False`` for
-            impure functions like ``np.random.random``.
+            impure functions like ``np.random.random``. Note that if both
+            ``actor`` and ``pure`` kwargs are set to True, then the value
+            of ``pure`` will be reverted to False, since an actor is stateful.
             See :ref:`pure functions` for more details.
         **kwargs
 
@@ -1919,7 +1921,7 @@ def submit(
             raise TypeError("First input to submit must be a callable function")
 
         actor = actor or actors
-        if pure is None:
+        if actor:
             pure = not actor
 
         if allow_other_workers not in (True, False, None):
@@ -1978,7 +1980,7 @@ def map(
         fifo_timeout="100 ms",
         actor=False,
         actors=False,
-        pure=None,
+        pure=True,
         batch_size=None,
         **kwargs,
     ):
@@ -2022,7 +2024,9 @@ def map(
             Alias for `actor`
         pure : bool (defaults to True)
             Whether or not the function is pure.  Set ``pure=False`` for
-            impure functions like ``np.random.random``.
+            impure functions like ``np.random.random``. Note that if both
+            ``actor`` and ``pure`` kwargs are set to True, then the value
+            of ``pure`` will be reverted to False, since an actor is stateful.
             See :ref:`pure functions` for more details.
         batch_size : int, optional (default: just one batch whose size is the entire iterable)
             Submit tasks to the scheduler in batches of (at most)
@@ -2100,7 +2104,7 @@ def map(
 
         key = key or funcname(func)
         actor = actor or actors
-        if pure is None:
+        if actor:
             pure = not actor
 
         if allow_other_workers and workers is None: