jorisvandenbossche commented on a change in pull request #9351:
URL: https://github.com/apache/arrow/pull/9351#discussion_r566220109



##########
File path: python/pyarrow/_dataset.pyx
##########
@@ -84,7 +84,25 @@ cdef CFileSource _make_file_source(object file, FileSystem 
filesystem=None):
 
 
 cdef class Expression(_Weakrefable):
-
+    """
+    A logical expression to be evaluated against some input.
+
+    To create an expression:
+     - Use the factory function ``pyarrow.dataset.scalar()`` to create a
+       scalar (not necessary when combined, see example below).
+     - Use the factory function ``pyarrow.dataset.field()`` to reference
+       a field (column in table).
+     - Compare fields and scalars with ``<``, ``<=``, ``==``, ``>=``, ``>``.
+     - Combine expressions using python operators ``&`` (logical and),
+       ``|`` (logical or) and ``~`` (logical not).
+       Note: python keywords ``and``, ``or`` and ``not`` do not work to 
combine expressions.
+
+    Examples:
+    --------
+    >>> from pyarrow.dataset import scalar, field

Review comment:
       In the other part of the docs, we use `import pyarrow.dataset as ds`, we 
should probably be consistent 
(https://arrow.apache.org/docs/python/dataset.html)

##########
File path: python/pyarrow/_dataset.pyx
##########
@@ -84,7 +84,25 @@ cdef CFileSource _make_file_source(object file, FileSystem 
filesystem=None):
 
 
 cdef class Expression(_Weakrefable):
-
+    """
+    A logical expression to be evaluated against some input.
+
+    To create an expression:
+     - Use the factory function ``pyarrow.dataset.scalar()`` to create a

Review comment:
       Can you leave a blank line above this one (to separate the text from the 
list)?
   
   And the `-` has one extra space before it as indentation, which needs to be 
removed in order to render it correctly with sphinx.
   
   (restructured text is quite picky ... ;))




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