DOC: Add glossary term for aes expression

Author: has2k1

doc/conf.py

@@ -435,6 +435,7 @@
     'geom': ':term:`geom`',
     'stat': ':term:`stat`',
     'position': ':term:`position`',
+    'expression': ':term:`expression`',
 }
 
 

doc/glossary.rst

@@ -15,3 +15,16 @@ Glossary of Common Terms
 
     position
         A subclass of :class:`~plotnine.positions.position.position`.
+
+    expression
+        A python expression wrapped in a string. The expression can
+        refer to variables in the user environment and columns in
+        the dataframe.
+
+        The following may be valid expressions::
+
+            'col1'
+            'col1 + col2'
+            'np.sin(col1)'
+            '"string-value"'
+

plotnine/aes.py

@@ -32,11 +32,11 @@ class aes(dict):
 
     Parameters
     ----------
-    x : str | array_like | scalar | str-expression
+    x : expression | array_like | scalar
         x aesthetic mapping
-    y : str | array_like | scalar | str-expression
+    y : expression | array_like | scalar
         y aesthetic mapping
-    \*\*kwargs : dict
+    **kwargs : dict
         Other aesthetic mappings
 
     Notes