add float(::PyObject) (#660)

* add float(::PyObject)

* check for __float__ method as a fallback

* whoops

Author: stevengj

src/conversions.jl

@@ -63,6 +63,15 @@ convert(::Type{T}, po::PyObject) where T<:Complex =
 
 convert(::Type{Nothing}, po::PyObject) = nothing
 
+function Base.float(o::PyObject)
+    a = PyAny(o)
+    if a isa PyObject
+        hasproperty(o, :__float__) && return o.__float__()
+        throw(ArgumentError("don't know how convert $o to a Julia floating-point value"))
+    end
+    return float(a)
+end
+
 #########################################################################
 # String conversions (both bytes arrays and unicode strings)
 

test/runtests.jl

@@ -26,7 +26,7 @@ pymodule_exists(s::AbstractString) = !ispynull(pyimport_e(s))
 # default integer type for PyAny conversions
 const PyInt = pyversion < v"3" ? Int : Clonglong
 
-@testset "PyCall" begin
+@testset "conversions" begin
     # conversion of NumPy scalars before npy_initialized by array conversions (#481)
     np = pyimport_e("numpy")
     if !ispynull(np) # numpy is installed, so test
@@ -569,6 +569,11 @@ const PyInt = pyversion < v"3" ? Int : Clonglong
 
     # issue #533
     @test py"lambda x,y,z: (x,y,z)"(3:6,4:10,5:11) === (PyInt(3):PyInt(6), PyInt(4):PyInt(10), PyInt(5):PyInt(11))
+
+    @test float(PyObject(1)) === 1.0
+    @test float(PyObject(1+2im)) === 1.0 + 2.0im
+    @test float(PyObject([1,2,3]))[2] === 2.0
+    @test_throws ArgumentError float(pybuiltin("type"))
 end
 
 ######################################################################