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.
Well yeah just because they kinda mean the same thing it doesn’t mean that they are the same. I can wholly understand why they won’t “fix” your inconvenience.
bool_via Numpy is its own object, and it’s fundamentally different fromboolin Python (which is itself a subclass ofint, whereasbool_is not).They are used similarly, but they’re similar in the same way a fork and a spork can both be used to eat spaghetti.
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 ?
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""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.Oh that makes sense. I didn’t consider it might be treated as a char
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
-
Data typing is important. If two types do not have the same in-memory representation but you treat them like they do, you’re inviting a lot of potential bugs and security vulnerabilities to save a few characters.
ETA: The WONTFIX is absolutely the correct response here. This would allow devs to shoot themselves in the foot for no real gain, eliminating the benefit of things like mypy. Type safety is your friend and will keep you from making simple mistakes.
Even if they do have the same in-memory representation, you may want to assert types as different just by name.
AccountID: u64
TransactionID: u64
have the same in-memory representation, but are not interchangeable.
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?
From 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.
Honestly, after having served on a Very Large Project with Mypy everywhere, I can categorically say that I hate it. Types are great, type checking is great, but applying it to a language designed without types in mind is a recipe for pain.
Adding types on an untyped project is hell. Greenfield stuff is usually pretty smooth sailing as far as I’m concerned…
