Show error message when user tries to install/run PlatformIO with Python 3

platformio/__init__.py

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import sys
+
 VERSION = (2, 7, "0.dev0")
 __version__ = ".".join([str(s) for s in VERSION])
 
@@ -31,3 +33,10 @@ __license__ = "Apache Software License"
 __copyright__ = "Copyright 2014-2015 Ivan Kravets"
 
 __apiurl__ = "http://api.platformio.org"
+
+
+if sys.version_info >= (3, 0, 0):
+    msg = ("PlatformIO version %s does not run under Python version %s.\n"
+           "Python 3 is not yet supported.\n")
+    sys.stderr.write(msg % (__version__, sys.version.split()[0]))
+    sys.exit(1)

setup.py

@@ -12,11 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
 from setuptools import find_packages, setup
 
 from platformio import (__author__, __description__, __email__, __license__,
-                        __title__, __url__, __version__, util)
+                        __title__, __url__, __version__)
 
 
 setup(