add check that dash was correctly imported and exit with helpful mess…

…age if failed (#177)

* add check that dash was imported and exit with useful message if not

* added test to check sys.exit(1) called when dash not import correctly

* fix wrong module name

dash_core_components/__init__.py

@@ -1,8 +1,17 @@
+from __future__ import print_function as _
+
 import os as _os
 import sys as _sys
+
 import dash as _dash
+
 from .version import __version__
 
+if not hasattr(_dash, 'development'):
+    print("Dash was not successfully imported. Make sure you don't have a file "
+          "named \n'dash.py' in your current directory.", file=_sys.stderr)
+    _sys.exit(1)
+
 _current_path = _os.path.dirname(_os.path.abspath(__file__))
 
 _components = _dash.development.component_loader.load_components(

test/test_dash_import.py

@@ -0,0 +1,23 @@
+import os
+import unittest
+
+
+class TestDashImport(unittest.TestCase):
+    def setUp(self):
+        with open('dash.py', 'w') as f:
+            pass        
+
+    def tearDown(self):
+        try:
+            os.remove('dash.py')
+            os.remove('dash.pyc')
+        except OSError:
+            pass
+
+    def test_dash_import(self):
+        """Test that program exits if the wrong dash module was imported"""
+
+        with self.assertRaises(SystemExit) as cm:
+            import dash_core_components
+
+        self.assertEqual(cm.exception.code, 1)

tox.ini

@@ -11,3 +11,5 @@ basepython={env:TOX_PYTHON_27}
 commands =
     python --version
     python -m unittest test.test_integration
+    python -m unittest test.test_dash_import
+