Python is dynamically but strongly typed. “2+True” is a type error; once something has a type, it has a type. There’s no WAT.
1. if list(): pass # implicit coercion from collection -> None -> bool. (Very uncommon weak typing and a terrible idea.)
2. a = 123; b = 4.5; c = a + b # implicit coercion from int -> float (Common but not universal weak typing. More often hides bugs than helps with ergonomics and readability but sometimes a worthwhile tradeoff.)
3. a = 1 + false # implicit coercion from bool to int (Common weak typing in scientific languages (for masking) and older C-family languages (for bit twiddling). However, that's still bad language design. Libraries/syntax sugar should special case masking and bit twiddling. You should not have global coersion between bool and int.)
4. etc.
x = 1
y = 2
print(x + y)
x = "no "
y = "types"
print(x + y)
x := 1
y := 2
x = "no"
y = "types"I do think my example code demonstrates why Go is easier to reason at scale than Python. Python is conflating assignment and type declaration. Go has = and :=, so it's crystal clear what's going on.
Dynamic typing doesn't rule out polymorphism.
void print(PyObject objects...)
Additionally, you could perfectly well have constants, or require variables to have a fixed type, in a dynamic language. You would just pay a cost at runtime to check the type on assignment.
I like the way Rust makes clear what are the different possibilities:
In Rust we use a macro to handle variadic arguments, but if it was just a case of supporting different types, not of supporting an arbitrary number of arguments we would've had three options for the type signature:
1. Monomorphic duck typing: `fn print(arg: &impl Debug)`. Here the compiler simply generates multiple print functions, one for every type the function gets called on. The exact concrete type is known at compile time.
2. Polymorphic dynamic dispatch (with dynamic sizing) duck typing: `fn print(arg: Box<dyn<Debug>>)`. Here the compiler generates a vtable and allocates on the heap. Only a type approximation is known at compile time, not the exact concrete type, but it still counts as static typing.
3. Dynamic typing: `fn print(arg: Box<dyn<Any>>)`. Note `Any` in stead of `Debug`. Full dynamic typing with the type completely unknown at compile time. Juck! But occasionally useful for prototyping or for FFI with dynamically typed languages.
Dynamic typing doesn't rule out polymorphism.
void print(PyObject objects...)
Here's a comment of mine that explains why Python is weakly typed: https://news.ycombinator.com/item?id=26354039.
Here's a comment of mine that explains why Python is weakly typed: https://news.ycombinator.com/item?id=26354039.