gnu: python-chai: Remove Python2 code.

* gnu/packages/patches/python-chai-drop-python2.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/python-xyz.scm (python-chai)[source]: Use it.

gnu/local.mk

@@ -1534,6 +1534,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/plasma-framework-fix-KF5PlasmaMacros.cmake.patch \
   %D%/packages/patches/ppsspp-disable-upgrade-and-gold.patch		\
   %D%/packages/patches/pthreadpool-system-libraries.patch	\
+  %D%/packages/patches/python-chai-drop-python2.patch		\
   %D%/packages/patches/sdcc-disable-non-free-code.patch		\
   %D%/packages/patches/sdl-pango-api_additions.patch		\
   %D%/packages/patches/sdl-pango-blit_overflow.patch		\

gnu/packages/patches/python-chai-drop-python2.patch

@@ -0,0 +1,32 @@
+Patch copied from Gentoo removing obsolete Python2 code.
+
+--- a/chai/chai.py
++++ b/chai/chai.py
+@@ -62,11 +62,6 @@
+             try:
+                 func(self, *args, **kwargs)
+             except UnexpectedCall as e:
+-                # if this is not python3, use python2 syntax
+-                if not hasattr(e, '__traceback__'):
+-                    from .python2 import reraise
+-                    reraise(
+-                        AssertionError, '\n\n' + str(e), sys.exc_info()[-1])
+                 exc = AssertionError('\n\n' + str(e))
+                 setattr(exc, '__traceback__', sys.exc_info()[-1])
+                 raise exc
+--- a/chai/python2.py
++++ b/chai/python2.py
+@@ -1,3 +0,0 @@
+-
+-def reraise(exc, msg, traceback):
+-    raise exc, msg, traceback
+--- a/chai.egg-info/SOURCES.txt
++++ b/chai.egg-info/SOURCES.txt
+@@ -10,7 +10,6 @@
+ chai/exception.py
+ chai/expectation.py
+ chai/mock.py
+-chai/python2.py
+ chai/spy.py
+ chai/stub.py
+ chai.egg-info/PKG-INFO

gnu/packages/python-xyz.scm

@@ -14561,7 +14561,8 @@ (define-public python-chai
               (uri (pypi-uri "chai" version))
               (sha256
                (base32
-                "1k6n6zbgrrs83crp6mr3yqj9zlv40b8rpisyrliwsq7naml2p3gz"))))
+                "1k6n6zbgrrs83crp6mr3yqj9zlv40b8rpisyrliwsq7naml2p3gz"))
+              (patches (search-patches "python-chai-drop-python2.patch"))))
     (build-system python-build-system)
     (home-page "https://github.com/agoragames/chai")
     (synopsis "Mocking framework for Python")