drop python 3.5 support

setup.py

@@ -37,7 +37,7 @@ def get_static_files(path):
 with open('README.rst') as fobj:
     long_description = "\n\n" + readme_note + "\n\n" + fobj.read()
 
-install_requires = ['python-dateutil>=2.7.5,<3', 'tenacity>=8,<9']
+install_requires = ['python-dateutil>=2.7.5,<3', 'tenacity>=8,<9', 'tornado>=5.0,<7']
 
 # Can't use python-daemon>=2.2.0 if on windows
 #     See https://pagure.io/python-daemon/issue/18
@@ -46,12 +46,6 @@ def get_static_files(path):
 else:
     install_requires.append('python-daemon')
 
-# Start from tornado 6, the minimum supported Python version is 3.5.2.
-if sys.version_info[:3] >= (3, 5, 2):
-    install_requires.append('tornado>=5.0,<7')
-else:
-    install_requires.append('tornado>=5.0,<6')
-
 if os.environ.get('READTHEDOCS', None) == 'True':
     # So that we can build documentation for luigi.db_task_history and luigi.contrib.sqla
     install_requires.append('sqlalchemy')
@@ -104,7 +98,6 @@ def get_static_files(path):
         'Intended Audience :: Developers',
         'Intended Audience :: System Administrators',
         'License :: OSI Approved :: Apache Software License',
-        'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{35,36,37,38,39,310,311,312}-{cdh,hdp,core,contrib,apache,aws,gcloud,postgres,unixsocket,azureblob,dropbox}, visualiser, docs, flake8
+envlist = py{36,37,38,39,310,311,312}-{cdh,hdp,core,contrib,apache,aws,gcloud,postgres,unixsocket,azureblob,dropbox}, visualiser, docs, flake8
 skipsdist = True
 
 [pytest]