warnings.warn() fails when looping over memcache_key_warnings()

[Rich Rauenzahn]

I think I found a bug in cache backends -- while running unit tests I was getting:

TypeError: 'type' object cannot be interpreted as an integer

I'm not sure why that exact message, but it arises here:

> .../virtualenv-3.6.8/lib64/python3.6/site-packages/django/core/cache/backends/base.py(250)validate_key()
    248         """
    249         for warning in memcache_key_warnings(key):
--> 250             warnings.warn(warning, CacheKeyWarning)
    251 
    252     def incr_version(self, key, delta=1, version=None):

I think the problem is that for loop is receiving a list of tuples, but they are interpreted as a list of strings:

ipdb> key
":1:<redacted but probably invalid for memcache"

# The generator returns tuples of (message, warning type)

ipdb> for x in memcache_key_warnings(key): print(x)
('Cache key contains characters that will cause errors if used with memcached: ":1:BuildAPI._request:(\'http://buildapi.eng.vmware.com/sb/build/1895757\', expire=10)"', <class 'django.core.cache.backends.base.CacheKeyWarning'>)

# But "warning" passed to warning.warn() is the tuple...  

ipdb> warning
('Cache key contains characters that will cause errors if used with memcached: ":1:BuildAPI._request:(\'http://buildapi.eng.vmware.com/sb/build/1895757\', expire=10)"', <class 'django.core.cache.backends.base.CacheKeyWarning'>)
ipdb>

I think it should be passing warning.warn(warning[0], warning[1]) or warning.warn(*warning)

Django 2.2.13 is what I am using.