gnu: python-memcached: Add patch to fix syntax warnings.

* gnu/packages/patches/python-memcached-syntax-warnings.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/python-xyz.scm (python-memcached)[source]: Add it.

Signed-off-by: Efraim Flashner <efraim@flashner.co.il>

gnu/local.mk

@@ -35,6 +35,7 @@
 # Copyright © 2020 Ryan Prior <rprior@protonmail.com>
 # Copyright © 2020 Jan Wielkiewicz <tona_kosmicznego_smiecia@interia.pl>
 # Copyright © 2020 Brice Waegeneire <brice@waegenei.re>
+# Copyright © 2020 Tanguy Le Carrour <tanguy@bioneland.org>
 #
 # This file is part of GNU Guix.
 #
@@ -1426,6 +1427,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/python-flint-includes.patch		\
   %D%/packages/patches/python-jedi-sort-project-test.patch	\
   %D%/packages/patches/python-libxml2-utf8.patch		\
+  %D%/packages/patches/python-memcached-syntax-warnings.patch	\
   %D%/packages/patches/python-mox3-python3.6-compat.patch	\
   %D%/packages/patches/python-testtools.patch			\
   %D%/packages/patches/python-packaging-test-arch.patch		\

gnu/packages/patches/python-memcached-syntax-warnings.patch

@@ -0,0 +1,24 @@
+Problem reported upstream:
+https://github.com/linsomniac/python-memcached/issues/176
+
+---
+ memcache.py | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/memcache.py b/memcache.py
+index 05b6657..b935681 100644
+--- a/memcache.py
++++ b/memcache.py
+@@ -1300,8 +1300,8 @@ class Client(threading.local):
+             key = key[1]
+         if key is None:
+             raise Client.MemcachedKeyNoneError("Key is None")
+-        if key is '':
+-            if key_extra_len is 0:
++        if key == '':
++            if key_extra_len == 0:
+                 raise Client.MemcachedKeyNoneError("Key is empty")
+
+             #  key is empty but there is some other component to key
+--
+2.26.2

gnu/packages/python-xyz.scm

@@ -11779,7 +11779,8 @@ running in.")
        (uri (pypi-uri "python-memcached" version))
        (sha256
         (base32
-         "0kvyapavbirk2x3n1jx4yb9nyigrj1s3x15nm3qhpvhkpqvqdqm2"))))
+         "0kvyapavbirk2x3n1jx4yb9nyigrj1s3x15nm3qhpvhkpqvqdqm2"))
+       (patches (search-patches "python-memcached-syntax-warnings.patch"))))
     (build-system python-build-system)
     (propagated-inputs `(("python-six" ,python-six)))
     (home-page