Implement pantsbuild#6450

Although our solution is going to end up releasing a separate wheel for Py2 vs Py3 for pantsbuild.pants, this is a good starting point for the changes we need to make.

src/python/pants/backend/python/pants_requirement.py

@@ -50,9 +50,7 @@ def __call__(self, name=None, dist=None):
                                       msg='The {} target only works for pantsbuild.pants '
                                           'distributions, given {}'.format(self.alias, dist))
 
-    # Update the environment marker in lockstep with other changes as described in
-    #   https://github.com/pantsbuild/pants/issues/6450
-    env_marker = "python_version>='2.7' and python_version<'3'"
+    env_marker = "python_version>='3.6' or (python_version>='2.7' and python_version<'3')"
 
     requirement = PythonRequirement(requirement="{key}=={version} ; {env_marker}"
                                     .format(key=dist,

src/python/pants/releases/packages.py

@@ -34,9 +34,7 @@ class Package(object):
   def __init__(self, name, target, bdist_wheel_flags=None):
     self.name = name
     self.target = target
-    # Update the --python-tag default in lockstep with other changes as described in
-    #   https://github.com/pantsbuild/pants/issues/6450
-    self.bdist_wheel_flags = bdist_wheel_flags or ("--python-tag", "py27")
+    self.bdist_wheel_flags = bdist_wheel_flags or ("--python-tag", "py27.py36.py37")
 
   def __lt__(self, other):
     return self.name < other.name
@@ -93,7 +91,7 @@ def find_platform_name():
   Package(
     "pantsbuild.pants",
     "//src/python/pants:pants-packaged",
-    bdist_wheel_flags=("--python-tag", "cp27", "--plat-name", find_platform_name()),
+    bdist_wheel_flags=("--python-tag", "cp27.cp36.cp37", "--plat-name", find_platform_name()),
   ),
   Package("pantsbuild.pants.testinfra", "//tests/python/pants_test:test_infra"),
 }