Make Julia exceptions wrapped in Python Exceptions more informative

src/callback.jl

@@ -39,7 +39,7 @@ function _pyjlwrap_call(f, args_::PyPtr, kw_::PyPtr)
 
         return pyreturn(ret)
     catch e
-        pyraise(e)
+        @pyraise e
     finally
         args.o = PyPtr_NULL # don't decref
     end

src/exception.jl

@@ -123,16 +123,21 @@ function pyexc_initialize()
     pyexc[PyIOError] = @pyglobalobjptr :PyExc_IOError
 end
 
+_showerror_string(io::IO, e, ::Nothing) = showerror(io, e)
+_showerror_string(io::IO, e, bt) = showerror(io, e, bt)
+
+# bt argument defaults to nothing, to delay dispatching on the presence of a
+# backtrace until after the try-catch block
 """
     showerror_string(e) :: String
 
 Convert output of `showerror` to a `String`.  Since this function may
 be called via Python C-API, it tries to not throw at all cost.
 """
-function showerror_string(e::T) where {T}
+function showerror_string(e::T, bt = nothing) where {T}
     try
         io = IOBuffer()
-        showerror(io, e)
+        _showerror_string(io, e, bt)
         return String(take!(io))
     catch
         try
@@ -163,15 +168,26 @@ function showerror_string(e::T) where {T}
     end
 end
 
-function pyraise(e)
+function pyraise(e, bt = nothing)
     eT = typeof(e)
     pyeT = haskey(pyexc::Dict, eT) ? pyexc[eT] : pyexc[Exception]
     ccall((@pysym :PyErr_SetString), Cvoid, (PyPtr, Cstring),
-          pyeT, string("Julia exception: ", showerror_string(e)))
+          pyeT, string("Julia exception: ", showerror_string(e, bt)))
 end
 
-function pyraise(e::PyError)
+# Second argument allows for backtraces passed to `pyraise` to be ignored.
+function pyraise(e::PyError, ::Vector = [])
     ccall((@pysym :PyErr_Restore), Cvoid, (PyPtr, PyPtr, PyPtr),
           e.T, e.val, e.traceback)
     e.T.o = e.val.o = e.traceback.o = C_NULL # refs were stolen
 end
+
+"""
+    @pyraise e
+
+Throw the exception `e` to Python, attaching a backtrace.  This macro should only be
+used in a `catch` block so that `catch_backtrace()` is valid.
+"""
+macro pyraise(e)
+    :(pyraise($(esc(e)), catch_backtrace()))
+end

src/io.jl

@@ -8,21 +8,21 @@
 # IOBase methods:
 
 # IO objects should raise IOError for unsupported operations or failed IO
-function ioraise(e)
+function ioraise(e, bt = nothing)
     if isa(e, MethodError) || isa(e, ErrorException)
         ccall((@pysym :PyErr_SetString), Cvoid, (PyPtr, Cstring),
               (pyexc::Dict)[PyIOError],
-              string("Julia exception: ", e))
+              showerror_string(e, bt))
     else
-        pyraise(e)
+        pyraise(e, bt)
     end
 end
 
 macro with_ioraise(expr)
     :(try
         $(esc(expr))
       catch e
-        ioraise(e)
+        ioraise(e, catch_backtrace())
       end)
 end
 

src/pyiterator.jl

@@ -134,7 +134,7 @@ const jlWrapIteratorType = PyTypeObject()
                 return pyreturn(item)
             end
         catch e
-            pyraise(e)
+            @pyraise e
         end
         return PyPtr_NULL
     end
@@ -149,7 +149,7 @@ else
                 return pyreturn(item)
             end
         catch e
-            pyraise(e)
+            @pyraise e
         end
         return PyPtr_NULL
     end
@@ -162,7 +162,7 @@ function pyjlwrap_getiter(self_::PyPtr)
         self = unsafe_pyjlwrap_to_objref(self_)
         return pystealref!(jlwrap_iterator(self))
     catch e
-        pyraise(e)
+        @pyraise e
     end
     return PyPtr_NULL
 end

src/pytype.jl

@@ -348,7 +348,7 @@ function pyjlwrap_repr(o::PyPtr)
         return pyreturn(o != C_NULL ? string("<PyCall.jlwrap ",unsafe_pyjlwrap_to_objref(o),">")
                         : "<PyCall.jlwrap NULL>")
     catch e
-        pyraise(e)
+        @pyraise e
         return PyPtr_NULL
     end
 end
@@ -395,7 +395,7 @@ function pyjlwrap_getattr(self_::PyPtr, attr__::PyPtr)
             end
         end
     catch e
-        pyraise(e)
+        @pyraise e
     finally
         attr_.o = PyPtr_NULL # don't decref
     end