问题
Assigning a Django Model's field to a value if it matches a condition.
g = Car.objects.get(pk=1234)
g.data_version = my_dict['dataVersion'] if my_dict else expression_false # Do nothing??
How do I do nothing in that case? We can't do if conditional else pass.
I know I can do:
if my_dict:
g.data_version = my_dict['dataVersion']
but I was wondering if there was a way to do inline expression_true if conditional else do nothing.
回答1:
No, you can't do exactly what you are describing, as it wouldn't make sense. You are assigning to the variable g.data_version... so you must assign something. What you describe would be like writing:
g.data_version = # There is nothing else here
Which is obviously invalid syntax. And really, there's no reason to do it. You should either do:
if my_dict:
g.data_version = my_dict['dataVersion']
or
g.data_version = my_dict['dataVersion'] if my_dict else None # or 0 or '' depending on what data_version should be.
Technically, you could also do:
g.data_version = my_dict['dataVersion'] if my_dict else g.data_version
if you only want to update g.data_version if your dict exists, but this is less readable and elegant than just using a normal if statement.
来源：https://stackoverflow.com/questions/25319053/python-inline-if-statement-else-do-nothing