Return None in functions that modify quantities in place

- Quantity.ito
- Quantity.ito_base_units

See:

https://docs.python.org/3.3/tutorial/datastructures.html#id3

BACKWARDS INCOMPATIBLE CHANGE

1 files changed, 4 insertions, 2 deletions

diff --git a/pint/quantity.py b/pint/quantity.py
index 2860f0a..467cff7 100644
--- a/pint/quantity.py
+++ b/pint/quantity.py
@@ -224,7 +224,8 @@ class _Quantity(object):
 
         self._magnitude = self._convert_magnitude(other, *contexts, **ctx_kwargs)
         self._units = other
-        return self
+
+        return None
 
     def to(self, other=None, *contexts, **ctx_kwargs):
         """Return Quantity rescaled to different units.
@@ -244,7 +245,8 @@ class _Quantity(object):
 
         self._magnitude = self._convert_magnitude(other)
         self._units = other
-        return self
+
+        return None
 
     def to_base_units(self):
         """Return Quantity rescaled to base units