One of the principles of the Pythonic style is: simple is better than complex.
But is it when you consider ambiguity and expressiveness too?
len(mylist) tells me it’s definitely a list and not null or whatever. It also tells me the intent of whoever writes the code was checking length.
If it requires a long article to explain, I’d certainly be hesitant to use and prefer. The question is, is it surprising or intuitive that the truthy becomes a length check. What do you want to express with your code. And who will read it, and what expectations and requirements do you want to require of them.
For sequence type objects, such as lists, their truth value is False if they are empty.
It’s just how pythonic code is written. All python developers know that not and bool can indicate that variable is either empty or null. They will also use the in operator and other python specific syntax.
Same with dictionaries, iterators (will consume the iterator!), and anything else that has a length.
I’ve actually had the string instead of list issue a number of times, because sometimes things get off and it’s hard to track down where things went wrong.
For this reason, I think type hints are the way to go. Use them consistently w/ a static analysis tool like pyright and you’ll catch a lot of these issues before running into cryptic error messages.
len(mylist) tells me it’s definitely a list and not null or whatever
Do you know what else can tell you it’s a list? Type hinting.
If I care about the distinction between None and an empty list, I’ll make separate checks. len(None) raises an exception, and most of the time that’s not what I want when checking whether there’s something in the list, so not x is generally preferred, especially when type hinting is used consistently enough to be reasonably sure I’m actually getting a list or None. If I get something else, that means things got really broken and they’ll likely get an exception alter (i.e. when doing anything list-like).
For sequence type objects, such as lists, their truth value is False if they are empty.
That’s generally exactly what I want. len(x) == 0 doesn’t tell you it’s a list, it just tells you it has __len__. So that could be a dict, list, or a number of other types that have a length, but aren’t lists.
Don’t rely on checks like that to tell you what type a thing is.
But is it when you consider ambiguity and expressiveness too?
len(mylist)tells me it’s definitely a list and not null or whatever. It also tells me the intent of whoever writes the code was checking length.If it requires a long article to explain, I’d certainly be hesitant to use and prefer. The question is, is it surprising or intuitive that the truthy becomes a length check. What do you want to express with your code. And who will read it, and what expectations and requirements do you want to require of them.
It’s just how pythonic code is written. All python developers know that
notandboolcan indicate that variable is either empty or null. They will also use theinoperator and other python specific syntax.foo = “potatoes!”
len(foo)
will give you the number of characters in the string. It’s not a surefire way to find a list at all!
Same with dictionaries, iterators (will consume the iterator!), and anything else that has a length.
I’ve actually had the string instead of list issue a number of times, because sometimes things get off and it’s hard to track down where things went wrong.
For this reason, I think type hints are the way to go. Use them consistently w/ a static analysis tool like
pyrightand you’ll catch a lot of these issues before running into cryptic error messages.Do you know what else can tell you it’s a list? Type hinting.
If I care about the distinction between None and an empty list, I’ll make separate checks.
len(None)raises an exception, and most of the time that’s not what I want when checking whether there’s something in the list, sonot xis generally preferred, especially when type hinting is used consistently enough to be reasonably sure I’m actually getting a list orNone. If I get something else, that means things got really broken and they’ll likely get an exception alter (i.e. when doing anything list-like).That’s generally exactly what I want.
len(x) == 0doesn’t tell you it’s a list, it just tells you it has__len__. So that could be adict,list, or a number of other types that have a length, but aren’t lists.Don’t rely on checks like that to tell you what type a thing is.