Minimum setuptools version should be 20.3 so Requirement has specifier attribute required by PR 355 (#391)
Minimum setuptools version should be 20.3 so Requirement has specifier attribute required by PR 355 (#391)

In #355 package.py was updated to assume that the Requirement class has the specifier attribute.

The specifier attribute wasn't added to the Requirement class until setuptools 20.3 pypa/setuptools@de4bdcf

The error when there is an older setuptools is

Exception message: Requirement instance has no attribute 'specifier'
sixninetynine/pex,jsirois/pex,kwlzn/pex,jsirois/pex,kwlzn/pex,sixninetynine/pex,pantsbuild/pex,pantsbuild/pex