Better error on empty typeshed directory

mypy/build.py

@@ -44,6 +44,7 @@
 from mypy.types import Type
 from mypy.version import __version__
 from mypy.plugin import Plugin, DefaultPlugin, ChainedPlugin
+from mypy.defaults import PYTHON3_VERSION_MIN
 
 
 # We need to know the location of this file to load data, but
@@ -279,12 +280,15 @@ def default_lib_path(data_dir: str,
         if os.path.isdir(auto):
             data_dir = auto
         typeshed_dir = os.path.join(data_dir, "typeshed")
-    # We allow a module for e.g. version 3.5 to be in 3.4/. The assumption
-    # is that a module added with 3.4 will still be present in Python 3.5.
-    versions = ["%d.%d" % (pyversion[0], minor)
-                for minor in reversed(range(pyversion[1] + 1))]
-    # E.g. for Python 3.2, try 3.2/, 3.1/, 3.0/, 3/, 2and3/.
-    # (Note that 3.1 and 3.0 aren't really supported, but we don't care.)
+    if pyversion[0] == 3:
+        # We allow a module for e.g. version 3.5 to be in 3.4/. The assumption
+        # is that a module added with 3.4 will still be present in Python 3.5.
+        versions = ["%d.%d" % (pyversion[0], minor)
+                    for minor in reversed(range(PYTHON3_VERSION_MIN[1], pyversion[1] + 1))]
+    else:
+        # For Python 2, we only have stubs for 2.7
+        versions = ["2.7"]
+    # E.g. for Python 3.5, try 3.5/, 3.4/, 3.3/, 3/, 2and3/.
     for v in versions + [str(pyversion[0]), '2and3']:
         for lib_type in ['stdlib', 'third_party']:
             stubdir = os.path.join(typeshed_dir, lib_type, v)
@@ -294,7 +298,11 @@ def default_lib_path(data_dir: str,
     # Add fallback path that can be used if we have a broken installation.
     if sys.platform != 'win32':
         path.append('/usr/local/lib/mypy')
-
+    if not path:
+        print("Could not resolve typeshed subdirectories. If you are using MyPy"
+              "from source, you need to run \"git submodule --init update\"."
+              "Otherwise your MyPy install is broken.", file=sys.stderr)
+        sys.exit(1)
     return path
 
 

mypy/defaults.py

@@ -1,4 +1,5 @@
 PYTHON2_VERSION = (2, 7)
 PYTHON3_VERSION = (3, 6)
+PYTHON3_VERSION_MIN = (3, 3)
 CACHE_DIR = '.mypy_cache'
 CONFIG_FILE = 'mypy.ini'