Find a source file in srcdir to allow to build outside of srcdir.
diff --git a/setup.py b/setup.py
index bbda7f2..126a49e 100644
--- a/setup.py
+++ b/setup.py
@@ -863,7 +863,7 @@
# Fredrik Lundh's cElementTree module. Note that this also
# uses expat (via the CAPI hook in pyexpat).
- if os.path.isfile('Modules/_elementtree.c'):
+ if os.path.isfile(os.path.join(srcdir, 'Modules', '_elementtree.c')):
define_macros.append(('USE_PYEXPAT_CAPI', None))
exts.append(Extension('_elementtree',
define_macros = define_macros,