On Thu, Oct 21, 2021 at 10:49:35AM +0200, Baptiste Carvello wrote:
Versions of this that rely on catching AttributeError are simply wrong and are an anti-pattern. They catch too much and silently turn errors into silent wrong behaviour.
PEP 505 does not fall into that trap.
This is not true as a general rule: the PEP 505 examples with `dict.get()` do catch too much.
The problem there is not the None-aware operators, but the use of dict.get. That's a good reason to re-think None-aware subscripting. dict?['key'] will still raise if you mistype the key, while dict.get does not. Even if we limit ourselves to dict.get: return obj?.get('spam')?.get('eggs') doesn't protect against mispellings of the keys, *due to dict.get*, but it does protect against mispelling "get" (unlikely). More importantly it also protects against type errors: obj['spam'] = {'eggs', value} # oops, a set, not a dict or equivalent. (I don't mean to limit this to just typos.) Now if we write: obj?.get('spam')?.get('eggs') the first attribute lookup will return a set and the second will fail because sets don't have a get method. Where as if we use exceptions: try: obj['spam]['eggs'] except (TypeError, KeyError): return None the error is silently suppressed and we get None when we should get a TypeError. -- Steve