GH-34428: [Python][Docs] Add docsstring for make_fragment

python/pyarrow/_dataset.pyx

@@ -891,8 +891,14 @@ cdef class FileFormat(_Weakrefable):
         filesystem : Filesystem, optional
             If `filesystem` is given, `file` must be a string and specifies
             the path of the file to read from the filesystem.
-        partition_expression : Expression
-            The filter expression.
+        partition_expression : Expression, optional
+            An expression that is guaranteed true for all rows in the fragment.  Allows
+            fragment to be potentially skipped while scanning with a filter.
+
+        Returns
+        -------
+        fragment : Fragment
+            The file fragment
         """
         if partition_expression is None:
             partition_expression = _true

python/pyarrow/_dataset_parquet.pyx

@@ -209,6 +209,27 @@ cdef class ParquetFileFormat(FileFormat):
 
     def make_fragment(self, file, filesystem=None,
                       Expression partition_expression=None, row_groups=None):
+        """
+        Make a FileFragment from a given file.
+
+        Parameters
+        ----------
+        file : file-like object, path-like or str
+            The file or file path to make a fragment from.
+        filesystem : Filesystem, optional
+            If `filesystem` is given, `file` must be a string and specifies
+            the path of the file to read from the filesystem.
+        partition_expression : Expression, optional
+            An expression that is guaranteed true for all rows in the fragment.  Allows
+            fragment to be potentially skipped while scanning with a filter.
+        row_groups : Iterable, optional
+            The indices of the row groups to include
+
+        Returns
+        -------
+        fragment : Fragment
+            The file fragment
+        """
         cdef:
             vector[int] c_row_groups