ggplot.add and ggplot.iadd both accept sequences

Triggered by the requirements for type-checking, these two have the
same signature. And it just makes sense!

REF: python/mypy#6225
     #648

Author: has2k1

doc/changelog.rst

@@ -5,6 +5,14 @@ v0.10.2
 -------
 (Not yet released)
 
+API Changes
+***********
+
+- :method:`~plotnine.ggplot.add` and :method:`~plotnine.ggplot.iadd` now
+  accept the same types of objects. In this change
+  :method:`~plotnine.ggplot.iadd` has gained the ability to accept a list
+  of objects.
+
 Bug Fixes
 *********
 

plotnine/ggplot.py

@@ -1,4 +1,5 @@
 import sys
+from collections.abc import Sequence
 from copy import deepcopy
 from itertools import chain
 from pathlib import Path
@@ -125,27 +126,38 @@ def __deepcopy__(self, memo):
     def __iadd__(self, other):
         """
         Add other to ggplot object
+
+        Parameters
+        ----------
+        other : object or Sequence
+            Either an object that knows how to "radd"
+            itself to a ggplot, or a list of such objects.
         """
+        if isinstance(other, Sequence):
+            for item in other:
+                item.__radd__(self, inplace=True)
+            return self
+        elif other is None:
+            return self
+
         try:
             return other.__radd__(self, inplace=True)
         except TypeError:
             return other.__radd__(self)
         except AttributeError as err:
-            if other is None:
-                return self.__add__(other)
             raise err
 
     def __add__(self, other):
         """
-        Add to ggitems from a list
+        Add to ggplot from a list
 
         Parameters
         ----------
-        other : object or list
+        other : object or Sequence
             Either an object that knows how to "radd"
             itself to a ggplot, or a list of such objects.
         """
-        if isinstance(other, list):
+        if isinstance(other, Sequence):
             self = deepcopy(self)
             for item in other:
                 self += item

tests/test_ggplot_internals.py

@@ -305,6 +305,23 @@ def test_adding_list_ggplot():
     assert isinstance(g.coordinates, coord_trans)
 
 
+def test_iadding_list_ggplot():
+    lst = [
+        geom_point(),
+        geom_point(aes('x+1', 'y+1')),
+        xlab('x-label'),
+        coord_trans()
+    ]
+    g = ggplot()
+    id_before = id(g)
+    g += lst
+    id_after = id(g)
+    assert id_before == id_after
+    assert len(g.layers) == 2
+    assert g.labels['x'] == 'x-label'
+    assert isinstance(g.coordinates, coord_trans)
+
+
 def test_adding_None():
     p = ggplot(df, aes('x', 'y')) + geom_point()
     p2 = p + None