use python list comprehension to update dictionary value
if you're using dict.update don't assign it to the original variable since it returns None
[a.update(price=0) for a in data if a['price']=='']
without assignment will update the list...
Assignments are statements, and statements are not usable inside list comprehensions. Just use a normal for-loop:
data = ...
for a in data:
if a['price'] == '':
a['price'] = 0
And for the sake of completeness, you can also use this abomination (but that doesn't mean you should):
data = ...
[a.__setitem__('price', 0 if a['price'] == '' else a['price']) for a in data]