setup.py: add python_requires

It gets used by pip>=9 to decide which version from pypi to install. Which means we can
more easily drop older Python versions without having to worry about breaking anyones setup.

Sadly our oldest supported system, Ubuntu Xenial, only has pip 8, so it will install
the newest version and fail anyway if we drop Python 3.5 support. We can at least
point users to update their pip in their virtual environments then.

https://packaging.python.org/guides/distributing-packages-using-setuptools/#python-requires

1 files changed, 2 insertions, 0 deletions

diff --git a/setup.py b/setup.py
index b9172131..6f6f86df 100755
--- a/setup.py
+++ b/setup.py
@@ -1272,6 +1272,8 @@ def main():
             "install_pkgconfig": install_pkgconfig,
         },
         install_requires=install_requires,
+        python_requires=(
+            '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, <4'),
         data_files=[
             ('include/pygobject-3.0', ['gi/pygobject.h']),
         ],