Explanation: Python is a programming language. Numpy is a library for python that makes it possible to run large computations much faster than in native python. In order to make that possible, it needs to keep its own set of data types that are different from python’s native datatypes, which means you now have two different bool types and two different sets of True and False. Lovely.
Mypy is a type checker for python (python supports static typing, but doesn’t actually enforce it). Mypy treats numpy’s bool_ and python’s native bool as incompatible types, leading to the asinine error message above. Mypy is “technically” correct, since they are two completely different classes. But in practice, there is little functional difference between bool and bool_. So you have to do dumb workarounds like declaring every bool values as bool | np.bool_ or casting bool_ down to bool. Ugh. Both numpy and mypy declared this issue a WONTFIX. Lovely.
Good meme, bad reasoning. Things like that are why JavaScript is hated. While it looks the same, It should never, and in ANY case be IMPLICITLY turned into another type.
So you have to do dumb workarounds like declaring every
boolvalues asbool | np.bool_or castingbool_down tobool.these dumb workarounds prevent you from shooting yourself on the foot and not allowing JS-level shit like
"1" + 2 === "12"The JS thing makes perfect sense though,
“1” is a string. You declared its type by using quotes.
myString = "1"in a dynamically typed language is identical to writingstring myString = "1"in a statically typed language. You declare it in the symbols used to write it instead of having to manually write outstringevery single time.2 is an integer. You know this because you used neither quotes nor a decimal place surrounding it. This is also explicit.
"1" + 2, if your interpreter is working correctly, should do the following-
identify the operands from left to right, including their types.
-
note that the very first operand in the list is a
stringtype as you explicitly declared it as such by putting it in quotes. -
cast the following operands to
stringif they are not already. -
use the string addition method to add operands together (in this case, this means concatenation).
In the example you provided,
"1" + 2is equivalent to"1" + "2", but you’re making the interpreter do more work.QED:
"1" + 2should, in fact,=== "12", and your lack of ability to handle a language where you declare types by symbols rather than spending extra effort writing the type out as a full english word is your own shortcoming. Learn to declare and handle types in dynamic languages better, don’t blame your own misgivings on the language.Signed, a software engineer.
TypeError is also a correct response, though, and I think many folks would say makes more sense. Is an unnecessary footgun
-
"1" + 2 === "12"is not unique to JS (sans the requirement for the third equals sign), it’s a common feature of multiple strongly typed languages. imho it’s fine.EDIT: I did some testing:
What it works in:
- JS
- TS
- Java
- C#
- C++
- Kotlin
- Groovy
- Scala
- PowerShell
What produces a number, instead of a string:
- PHP
- SQL
- Perl
- VB
- Lua
What it doesn’t work in:
- R
- C
- Go
- Swift
- Rust
- Python
- Pascal
- Ruby
- Objective C
- Julia
- Fortran
- Ada
- Dart
- D
- Elixir
And MATLAB appears to produce 51, wtf idk
And MATLAB appears to produce 51, wtf idk
The numeric value of the ‘1’ character (the ASCII code / Unicode code point representing the digit) is 49. Add 2 to it and you get 51.
C (and several related languages) will do the same if you evaluate
'1' + 2.
Well, C has implicit casts, and it’s not that weird (although results in some interesting bugs in certain circumstances). Python is also funny from time to time, albeit due to different reasons (e.g.
-5**2is apparently -25 because of the order of operations)I don’t see how your example is ‘funny’. That’s what you expect to get. -52 is -25. (-5)2 = 25.
And how’s that different from js’s
"1" + 2? One can always convert a number to string, and only sometimes – a string to a number, so it’s pretty logical to go with the former.
-5**2 is apparently -25 because of the order of operations)
Which is correct
Well, the link doesn’t load for me, so if that’s smth related to python and not a justification of the behavior from math’s pov, I know that’s expected. Hence,
because of the order of operations
But just as well is “1” + 2.
This explanation is pretty clear cut
What exactly is your use case for treating
np.bool_andboolas interchangeable? Ifnp.bool_isn’t a subclass ofboolaccording to Python itself, then allowing one to be used where the other is expected just seems like it would prevent mypy from noticing bugs that might arise from code that expects aboolbut gets annp.bool_(or vice versa), and can only handle one of those correctly.mpy and numpy are opensource. You could always implement the fix you need yourself ?
They’ve declared it as WONTFIX, so unless you’re suggesting that OP creates a fork of numpy, that’s not going to work.
Well, yes exactly
- Create fixes
- Request merge. assume denied
- Fork numpy and add your changes there
- after just continue to pull new changes over from source of the fork and deal with any merge issues with the fix
That’s incredibly inconvenient.
Thats what adding strong typing does for you
I/O Issues are problems that come with the territory for scripting languages like python. Its why I prefer to use bash for scripting instead, because in bash, all I/O are strings. And if there are ever any conflicts, well that’s what awk/sed/Perl are for.
So many people here explaining why Python works that way, but what’s the reason for numpy to introduce its own boolean? Is the Python boolean somehow insufficient?
here’s a good question answer on this topic
https://stackoverflow.com/questions/18922407/boolean-and-type-checking-in-python-vs-numpy
plus this is kinda the tools doing their jobs.
bool_exists for whatever reason. its not aboolbut functionally equivalent.the static type checker mpy, correctly, states
bool_andboolaren’t compatible. in the same way other type different types aren’t compatibleFrom numpy’s docs:
The bool_ data type is very similar to the Python bool but does not inherit from it because Python’s bool does not allow itself to be inherited from, and on the C-level the size of the actual bool data is not the same as a Python Boolean scalar.
and likewise:
The int_ type does not inherit from the int built-in under Python 3, because type int is no longer a fixed-width integer type.
What years of dynamic typing brainrot does to mf
That’s actually a quite bad way of naming types, even if someone really insists on using 32 bit integers for bools for “performance” reasons.
Why use bool when you can use int?
just never #define true 0
