[pypy-dev] Pip Install Fails Due to cppyy-backend setup.py Bug

Parker Boyce parkersboyce at gmail.com
Tue Sep 26 22:07:20 EDT 2017

I recently had reason to try to install cppyy using Python 3 and pip. With
the use of the wheels for cppyy-cling the process went smoothly enough
until pip tried to build cppyy-backend
<https://pypi.python.org/pypi/cppyy-backend/0.2.0>. Building this package
by itself results in the following error message;

$ python3 setup.py build
running build
running build_ext
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall
-Wstrict-prototypes -g -fstack-protector-strong -Wformat
-Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC
-I/usr/include/python3.5m -c src/clingwrapper.cxx -o
build/temp.linux-x86_64-3.5/src/clingwrapper.o -std=c++11 -O2
cc1plus: warning: command line option ‘-Wstrict-prototypes’ is valid for
C/ObjC but not for C++
In file included from src/clingwrapper.cxx:4:0:
src/callcontext.h:11:20: fatal error: Rtypes.h: No such file or directory
compilation terminated.
error: command 'x86_64-linux-gnu-gcc' failed with exit status 1

A careful look at the command line argument for gcc reveals a mangled
include argument,
-Ib'/usr/local/lib/python3.5/dist-packages/cppyy_backend/include'. This is
a binary literal string introduced by the output of a system call,
"cling-config --cppflags". The functions in the subprocess module return
'bytes' objects in Python 3. In this case the return value from
'check_output' was appended wholesale into the 'include_dirs' argument of
your extension, and the representation thereof was used in turn to build
the function call to gcc. (The representation being a binary literal string)

To fix this the bytes object returned by subprocess.check_output needs to
be decoded to either 'utf-8' or 'ascii', preferably the former as Python 3
uses unicode literals. This can be accomplished by appending
'.decode("utf-8")' to line 28;

--- /home/parker/Documents/cppyy/cppyy-backend-0.2.0/setup.py Fri Sep 22
12:25:29 2017
+++ /home/parker/Documents/cppyy/cppyy-backend-0.2.0/setup.py.patched Tue
Sep 26 19:37:50 2017
@@ -25,7 +25,7 @@
     if root_install:
         return os.path.join(root_install, 'include')
     cli_arg = subprocess.check_output(['cling-config', '--cppflags'])
-    return cli_arg[2:-1]
+    return cli_arg[2:-1].decode("utf-8")

 class my_build_cpplib(_build_ext):
     def build_extension(self, ext):

With this patch pip will be able to build the cppyy-backend package from
source on Python 2 or 3, and pip installing cppyy will not require user

P.S. The "Comments and Bugs" section of the cppyy docs directs the reader
to a repository with issue tracking turned off, which is why you're getting
this email instead.
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