I hope I don't reinvent the wheel but the solution is fairly short. And, superfun to code.
def merge(source, destination):
"""
run me with nosetests --with-doctest file.py
>>> a = { 'first' : { 'all_rows' : { 'pass' : 'dog', 'number' : '1' } } }
>>> b = { 'first' : { 'all_rows' : { 'fail' : 'cat', 'number' : '5' } } }
>>> merge(b, a) == { 'first' : { 'all_rows' : { 'pass' : 'dog', 'fail' : 'cat', 'number' : '5' } } }
True
"""
for key, value in source.items():
if isinstance(value, dict):
# get node or create one
node = destination.setdefault(key, {})
merge(value, node)
else:
destination[key] = value
return destination
So the idea is to copy the source to the destination, and every time it's a dict in the source, recurse. So indeed you will have a bug if in A a given element contains a dict and in B any other type.
[EDIT] as said in comments the solution was already here : https://stackoverflow.com/a/7205107/34871
