3 ms·

"The following values are considered false: * None * False * zero of any numeric type, for example, 0, 0L, 0.0, 0j. * any empty sequence, for example, '', (

"The following values are considered false: * None * False * zero of any numeric type, for example, 0, 0L, 0.0, 0j. * any empty sequence, for example, '', (), []. * any empty mapping, for example, {}. * instances of user-defined classes, if the class defines a __nonzero__() or __len__() method, when that method returns the integer zero or bool value False." This really does not strike me as being simple. I personally don't find these shortcuts to be worthwhile. The best approach is that boolean is a separate type, true is true, false is false, and any attempt to use any other type as the predicate of a control flow statement is a (preferably compile-time) error. Writing `if x != 0` is not a large burden.

raverbashing 7y ago
> I personally don't find these shortcuts to be worthwhile They are, because they are the difference between driving with the parking brake on or not. Other languages don't have this so that's why people might not see the value in it first. > Writing `if x != 0` is not a large burden If you're comparing what can only be an int value, then it's not a burden. When your variable can assume multiple values, explicitly comparing it with multiple possibilities is a burden: Examples: - Your variable is optional and/or is a sequence that might be empty - You're using .get() in a dictionary One of the signs someone is unfamiliar with Python is doing multiple comparisons when only `if x:` would suffice
- mikeash 7y ago
  I've worked in a lot of different languages, from ones that work the way I prefer all the way to Python-style languages where anything is a predicate and there are a bunch of semi-arbitrary rules about what qualifies as "false." This isn't a lack of familiarity talking. Regarding your examples, having an optional sequence is probably not the correct move anyway. Is there actually a semantic difference between no sequence and an empty sequence? If not, the variable should be non-optional. If so, then glossing over those differences by writing `if x` to implicitly check both conditions is unclear. Not sure what you're referring to with get() in a dictionary. I understand that good Python style is considered to be one where you take advantage of the language's notion of truthiness, but I disagree with its whole approach.
  - raverbashing 7y ago
    > Is there actually a semantic difference between no sequence and an empty sequence? It really depends on your function, but you might want to have the function behave differently if given an empty list rather than no list. One very common case for doing that is when you want to facilitate unit testing of a function. > Not sure what you're referring to with get() in a dictionary. A very common case, in which you don't care if the element is not present or it is a "False" element.
    - mikeash 7y ago
      Behaving differently on an empty list than on no list is a huge smell. That's really weird and unexpected behavior. Doing it for testing is even weirder. If you're fetching an element from a dictionary and want not-present to be the same as some false value, fetch with a default value (in Python, pass a second parameter to get()) that you want to see when there's nothing present. Or just extract the value and check for nil or empty separately, nothing wrong with being explicit.
  - jhayward 7y ago
    There are Python idioms for exactness, and idioms for truthiness. When in a situation where it's possibly ambiguous to test truthiness 'if x is None:' or 'if x is True': is completely unambiguous. Most code doesn't need that and the truthiness nature of various data types is helpful in writing clear code.
- fhars 7y ago
  To me it looks more like the difference between driving with a working brake or without.

raverbashing 7y ago

> I personally don't find these shortcuts to be worthwhile They are, because they are the difference between driving with the parking brake on or not. Other languages don't have this so that's why people might not see the value in it first. > Writing `if x != 0` is not a large burden If you're comparing what can only be an int value, then it's not a burden. When your variable can assume multiple values, explicitly comparing it with multiple possibilities is a burden: Examples: - Your variable is optional and/or is a sequence that might be empty - You're using .get() in a dictionary One of the signs someone is unfamiliar with Python is doing multiple comparisons when only `if x:` would suffice

mikeash 7y ago
I've worked in a lot of different languages, from ones that work the way I prefer all the way to Python-style languages where anything is a predicate and there are a bunch of semi-arbitrary rules about what qualifies as "false." This isn't a lack of familiarity talking. Regarding your examples, having an optional sequence is probably not the correct move anyway. Is there actually a semantic difference between no sequence and an empty sequence? If not, the variable should be non-optional. If so, then glossing over those differences by writing `if x` to implicitly check both conditions is unclear. Not sure what you're referring to with get() in a dictionary. I understand that good Python style is considered to be one where you take advantage of the language's notion of truthiness, but I disagree with its whole approach.
- raverbashing 7y ago
  > Is there actually a semantic difference between no sequence and an empty sequence? It really depends on your function, but you might want to have the function behave differently if given an empty list rather than no list. One very common case for doing that is when you want to facilitate unit testing of a function. > Not sure what you're referring to with get() in a dictionary. A very common case, in which you don't care if the element is not present or it is a "False" element.
  - mikeash 7y ago
    Behaving differently on an empty list than on no list is a huge smell. That's really weird and unexpected behavior. Doing it for testing is even weirder. If you're fetching an element from a dictionary and want not-present to be the same as some false value, fetch with a default value (in Python, pass a second parameter to get()) that you want to see when there's nothing present. Or just extract the value and check for nil or empty separately, nothing wrong with being explicit.
- jhayward 7y ago
  There are Python idioms for exactness, and idioms for truthiness. When in a situation where it's possibly ambiguous to test truthiness 'if x is None:' or 'if x is True': is completely unambiguous. Most code doesn't need that and the truthiness nature of various data types is helpful in writing clear code.
fhars 7y ago
To me it looks more like the difference between driving with a working brake or without.