dogpile.cache is not compatible with decorator<4.0.0

[vashirov]

decorator module has decorate function, which doesn't exist in versions <4.0.0 (see release notes https://github.com/micheles/decorator/blob/4.0.0/documentation.rst#what-s-new)

But dogpile.cache doesn't explicitly specify the version of decorator module in setup.py:

dogpile.cache/setup.py

Line 59 in 4346981

install_requires=["decorator"],

So if decorator-3.4.0 is installed on the system, it satisfies the dependency chain, but dogpile.cache is not functional with it:

    sdk = importlib.import_module('openstack')                                                                                                                                
  File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in import_module                                                                                                
    __import__(name)                                                                                                                                                          
  File "/usr/lib/python2.7/site-packages/openstack/__init__.py", line 17, in <module>                                                                                         
    import openstack.connection                                                                                                                                               
  File "/usr/lib/python2.7/site-packages/openstack/connection.py", line 187, in <module>                                                                                      
    from openstack.cloud import openstackcloud as _cloud                                                                                                                      
  File "/usr/lib/python2.7/site-packages/openstack/cloud/openstackcloud.py", line 21, in <module>                                                                             
    import dogpile.cache                                                                                                                                                      
  File "/usr/lib/python2.7/site-packages/dogpile/cache/__init__.py", line 1, in <module>                                                                                      
    from .region import CacheRegion, register_backend, make_region  # noqa                                                                                                    
  File "/usr/lib/python2.7/site-packages/dogpile/cache/region.py", line 15, in <module>                                                                                       
    from decorator import decorate     

[zzzeek]

4.0.0 was July 2015 so this issue is unlikely to have wide impact

[zzzeek]

confirm 4.0.0 starts working

[sqla-tester]

Mike Bayer has proposed a fix for this issue in the master branch:

Pin minimum decorator version at 4.0.0 https://gerrit.sqlalchemy.org/1414