Adds tests (and fixes) for the dtype invariant.

docs/src/juliacall-reference.md

@@ -202,9 +202,9 @@ jl.Vector[jl.Int]()
 ```
 
 Some Julia types can be converted to corresponding numpy dtypes like `numpy.dtype(jl.Int)`.
-Supports primitive types: `Bool`, `IntXX`, `UIntXX`, `FloatXX`, `ComplexFXX`,
-`NumpyDates.InlineDateTime64{unit}` and `NumpyDates.InlineTimeDelta64{unit}`. Also
-supports tuples, named tuples and structs of these.
+Supports `Bool`, `IntXX`, `UIntXX`, `FloatXX`, `ComplexFXX`,
+`NumpyDates.InlineDateTime64{unit}` and `NumpyDates.InlineTimeDelta64{unit}`, plus
+`Tuple`s and `NamedTuple`s of these.
 `````
 
 `````@customdoc

src/JlWrap/array.jl

@@ -187,7 +187,7 @@ pybufferformat(::Type{T}) where {T} =
         T == Complex{Cdouble} ? "Zd" :
         T == Bool ? "?" :
         T == Ptr{Cvoid} ? "P" :
-        if isstructtype(T) && isconcretetype(T) && allocatedinline(T)
+        if (T <: Union{Tuple,NamedTuple}) && isstructtype(T) && isconcretetype(T) && allocatedinline(T)
             n = fieldcount(T)
             flds = []
             for i = 1:n
@@ -234,7 +234,7 @@ pyjlarray_isarrayabletype(::Type{NamedTuple{names,types}}) where {names,types} =
 
 const PYTYPESTRDESCR = IdDict{Type,Tuple{String,Py}}()
 
-pytypestrdescr(::Type{T}) where {T} =
+function pytypestrdescr(::Type{T}) where {T}
     get!(PYTYPESTRDESCR, T) do
         c = Utils.islittleendian() ? '<' : '>'
         if T == Bool
@@ -275,7 +275,7 @@ pytypestrdescr(::Type{T}) where {T} =
                 u == NumpyDates.UNBOUND_UNITS ? "" :
                 m == 1 ? "[$(Symbol(u))]" : "[$(m)$(Symbol(u))]"
             ("$(c)$(tc)8$(us)", PyNULL)
-        elseif isstructtype(T) && isconcretetype(T) && Base.allocatedinline(T)
+        elseif (T <: Union{Tuple,NamedTuple}) && isstructtype(T) && isconcretetype(T) && Base.allocatedinline(T)
             n = fieldcount(T)
             flds = []
             for i = 1:n
@@ -298,6 +298,7 @@ pytypestrdescr(::Type{T}) where {T} =
             ("", PyNULL)
         end
     end
+end
 
 pyjlarray_array__array(x::AbstractArray) = x isa Array ? Py(nothing) : pyjl(Array(x))
 pyjlarray_array__pyobjectarray(x::AbstractArray) = pyjl(PyObjectArray(x))

src/JlWrap/type.jl

@@ -11,22 +11,49 @@ function pyjltype_getitem(self::Type, k_)
     end
 end
 
+const PYNUMPYDTYPE = IdDict{Type,Py}()
+
 function pyjltype_numpy_dtype(self::Type)
-    typestr, descr = pytypestrdescr(self)
-    if isempty(typestr)
-        errset(pybuiltins.AttributeError, "__numpy_dtype__")
-        return PyNULL
+    ans = get!(PYNUMPYDTYPE, self) do
+        typestr, descr = pytypestrdescr(self)
+        # unsupported type
+        if typestr == ""
+            return PyNULL
+        end
+        np = pyimport("numpy")
+        # simple scalar type
+        if pyisnull(descr)
+            return np.dtype(typestr)
+        end
+        # We could juse use np.dtype(descr), but when there is padding, np.dtype(descr)
+        # changes the names of the padding fields from "" to "f{N}". Using this other
+        # dtype constructor avoids this issue and preserves the invariant:
+        #   np.dtype(eltype(array)) == np.array(array).dtype
+        names = []
+        formats = []
+        offsets = []
+        for i = 1:fieldcount(self)
+            nm = fieldname(self, i)
+            push!(names, nm isa Integer ? "f$(nm-1)" : String(nm))
+            ts, ds = pytypestrdescr(fieldtype(self, i))
+            push!(formats, pyisnull(ds) ? ts : ds)
+            push!(offsets, fieldoffset(self, i))
+        end
+        return np.dtype(
+            pydict(
+                names = pylist(names),
+                formats = pylist(formats),
+                offsets = pylist(offsets),
+                itemsize = sizeof(self),
+            ),
+        )
     end
-    np = pyimport("numpy")
-    if pyisnull(descr)
-        return np.dtype(typestr)
-    else
-        return np.dtype(descr)
+    if pyisnull(ans)
+        errset(pybuiltins.AttributeError, "__numpy_dtype__")
     end
+    return ans
 end
 
-pyjl_handle_error_type(::typeof(pyjltype_numpy_dtype), x, exc) = pybuiltins.AttributeError
-
 function init_type()
     jl = pyjuliacallmodule
     pybuiltins.exec(

test/JlWrap.jl

@@ -510,22 +510,28 @@ end
                 (Tuple{Int32, Int32}, pylist([("f0", "int32"), ("f1", "int32")])),
                 (@NamedTuple{}, pylist()),
                 (@NamedTuple{x::Int32, y::Int32}, pylist([("x", "int32"), ("y", "int32")])),
-                (Pair{Int32, Int32}, pylist([("first", "int32"), ("second", "int32")])),
             ]
                 @test pyeq(Bool, pygetattr(pyjl(t), "__numpy_dtype__"), np.dtype(d))
-                @test pyeq(Bool, np.dtype(pyjl(t)), np.dtype(d))
+                @test pyeq(Bool, np.dtype(t), np.dtype(d))
+                # test the invariant np.dtype(eltype(array)) == np.array(array).dtype
+                @test isequal(np.dtype(t), np.array(t[]).dtype)
             end
 
             # unsupported cases
             @testset "$t -> AttributeError" for t in [
-                # non-primitives or mutables
+                # structs / mutables
+                Pair,
+                Pair{Int,Int},
                 String,
                 Vector{Int},
                 # pointers
                 Ptr{Cvoid},
                 Ptr{Int},
                 # PyPtr specifically should NOT be interpreted as np.dtype("O")
                 PythonCall.C.PyPtr,
+                # tuples containing illegal things
+                Tuple{String},
+                Tuple{Pair{Int,Int}},
             ]
                 err = try
                     pygetattr(pyjl(t), "__numpy_dtype__")