Link refers number of changed features in a layer under edit mode so, if you commit changes, buffer (QgsVectorLayerEditBuffer object) will be lost. Complete procedure is as follows:
1) Load layer and in Python Console:
>>>layer = iface.activeLayer()
>>>buffer = layer.editBuffer()
>>>buffer #for corroborating object was produced
<qgis._core.QgsVectorLayerEditBuffer object at 0x7f81da97c948>
2) Click in "Toggle Editing button", open attributes table and make some changes in it; don't commit them. In my case, I only changed in my layer the first id feature. So, following command produces:
>>>buffer.changedAttributeValues()
{0: {0: 1}}
If a new change is produced, but I commit it, result is as follows:
>>>buffer.changedAttributeValues()
Traceback (most recent call last):
File "/usr/lib/python3.7/code.py", line 90, in runcode
exec(code, self.locals)
File "<input>", line 1, in <module>
RuntimeError: wrapped C/C++ object of type QgsVectorLayerEditBuffer has been deleted
For producing several consecutive changes, I change layer id three times in two records:
buffer = layer.editBuffer()
buffer.changedAttributeValues()
{0: {0: 3}, 1: {0: 2}}
However, only two changes were computed because layer has only two features.