Moved dependency check to runtime. Fixes #40.

CHANGES.rst

@@ -1,3 +1,9 @@
+4.2
+===
+
+* #40: Remove declared dependency and instead assert it at
+  run time.
+
 4.1
 ===
 

ptr.py

@@ -93,6 +93,18 @@ def initialize_options(self):
 		self.index_url = None
 		self.allow_hosts = None
 		self.addopts = []
+		self.ensure_setuptools_version()
+
+	@staticmethod
+	def ensure_setuptools_version():
+		"""
+		Due to the fact that pytest-runner is often required (via
+		setup-requires directive) by toolchains that never invoke
+		it (i.e. they're only installing the package, not testing it),
+		instead of declaring the dependency in the package
+		metadata, assert the requirement at run time.
+		"""
+		pkg_resources.require('setuptools>=27.3')
 
 	def finalize_options(self):
 		if self.addopts:

setup.py

@@ -32,7 +32,7 @@
 	py_modules=['ptr'],
 	python_requires='>=2.7,!=3.0,!=3.1',
 	install_requires=[
-		'setuptools>=27.3',
+		# setuptools 27.3 is required at run time
 	],
 	extras_require={
 		'testing': [