Py is always showable as text/plain

Author: Christopher Doris

src/Py.jl

@@ -265,6 +265,8 @@ end
 Base.show(io::IO, mime::MIME, o::Py) = pyshow(io, mime, o)
 Base.show(io::IO, mime::MIME"text/csv", o::Py) = pyshow(io, mime, o)
 Base.show(io::IO, mime::MIME"text/tab-separated-values", o::Py) = pyshow(io, mime, o)
+
+Base.showable(::MIME"text/plain", ::Py) = true
 Base.showable(mime::MIME, o::Py) = pyshowable(mime, o)
 
 Base.getproperty(x::Py, k::Symbol) = pygetattr(x, string(k))