kytta, 28 days ago

@tonybaloney because otherwise:

username = request.form.get("username", None)
if not username:
return "Bad Request", 400

Full Name: John False
Username: false

Registration failed: 400 Bad Request

tonybaloney, 27 days ago

@kytta I understand the truthiness of types, but for some reason I thought bool() would have some logic for friendly string-to-bool checks.

kytta, 26 days ago

@tonybaloney sounds like a hack, but would json.loads("false") not be kind of a "friendly" string-to-bool conversion? 😂

tonybaloney, 26 days ago

@kytta I prefer that over eval()

cliffordheath, 28 days ago

@tonybaloney that should have been four exceptions l

stfn, 28 days ago

@cliffordheath @tonybaloney why do you think so?

cliffordheath, 27 days ago

@stfn @tonybaloney Type conversion is not the same thing as validating user input. It must always succeed, or throw an exception. No unrecognised or imprecise input should succeed

stfn, 27 days ago

@cliffordheath @tonybaloney not sure what you mean. The examples above are simple type casting. A non-empty string is a truthy value. Casting a truthy value into a bool gives you True. Simple enough.

cliffordheath, 27 days ago

@stfn @tonybaloney Type conversions are reversible, they round-trip (bijection). A language that doesn't distinguish between down-casting and type conversion is not a safe language. If ("0"!="false") then bool("0") should not = bool("false"). I used to think think otherwise but participated in enough war stories to change my mind!

stfn, 27 days ago

@cliffordheath @tonybaloney i do not agree. You are talking about different things.

"0" != "False" you are comparing the values of strings, and they are different, so it is True.

bool("0") == bool("False") you are comparing the bool evaluations of two strings. And bool of a non-empty string is true so true == true.

Python has the concept of "truthy" values. Anything apart from False, None, integer 0 and empty string will evaluate to True

cliffordheath, 26 days ago

@stfn @tonybaloney Young padawan, I do understand truthiness, having built my first compiler 45 years ago, and coded every day since, in dozens of languages. This seductive concept is wrong-headed in ways that apparently cannot be taught, but must be learned. I wish you every success

stfn, 26 days ago

@cliffordheath @tonybaloney I am thankful for your input, it's always good to listen to people with more experience, you gave me a good food for thought

bignose, 28 days ago

@tonybaloney

Because any non-empty string evaluates true.

>>> if "false":
... print("A non-empty string evaluates true")
... else:
... print("and it'll never evaluate false")
...
A non-empty string evaluates true

chrisjrn, 28 days ago

@tonybaloney see also: Criticisms of JavaScript?