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Then make it explicit:
if l is None: raise ValueError("Must provide a valid value for...")
Having an attribute or type error rarely provides the right amount of context to immediately recognize the error, especially if it’s deep inside the application. A lot of our old code makes stupid errors like
TypeError: operator - not defined on types NoneType and float
, because someone screwed up somewhere and wasn’t strict on checks. Don’t reply on implicit exceptions, explicitly raise them so you can add context, because sometimes stacktraces get lost and all you have is the error message.But in my experience, the practical difference between
[]
andNone
is essentially zero, except in a few cases, and those should stand out. I have a few places with logic like this:if l is None: raise MyCustomInvalidException("Must provide a list") if not l: # nothing to do return
For example, if I make a task runner, an empty list could validly mean no arguments, while a null list means the caller screwed up somewhere and probably forgot to provide them.
Explicit is better than implicit, and simple is better than complex.