Fix activate_this.py does not exist, python-mode#406

pymode/virtualenv.py

@@ -1,6 +1,8 @@
 """ Support virtualenv in pymode. """
 
-import os.path
+import os
+import sys
+import site
 
 from .environment import env
 
@@ -25,13 +27,44 @@ def enable_virtualenv():
         activate_this = os.path.join(
             os.path.join(path, 'Scripts'), 'activate_this.py')
 
-    f = open(activate_this)
     try:
-        source = f.read()
-        exec(compile(  # noqa
-            source, activate_this, 'exec'), dict(__file__=activate_this))
-        env.message('Activate virtualenv: ' + path)
-        env.let('g:pymode_virtualenv_enabled', path)
-        return True
-    finally:
-        f.close()
+        with open(activate_this) as f:
+            source = f.read()
+            exec(compile(  # noqa
+                source, activate_this, 'exec'), dict(__file__=activate_this))
+    except IOError:
+        _activate_env_from_path(path)
+
+    env.message('Activate virtualenv: ' + path)
+    env.let('g:pymode_virtualenv_enabled', path)
+    return True
+
+
+def _activate_env_from_path(env_path):
+    """ Fix when `activate_this.py` does not exist.
+
+        For Python 3.3 and newer, a new command-line tool `pyvenv` create venv
+        will not provide 'activate_this.py'.
+    """
+    prev_sys_path = list(sys.path)
+
+    if sys.platform == 'win32':
+        site_packages_paths = [os.path.join(env_path, 'Lib', 'site-packages')]
+    else:
+        lib_path = os.path.join(env_path, 'lib')
+        site_packages_paths = [os.path.join(lib_path, lib, 'site-packages')
+                               for lib in os.listdir(lib_path)]
+    for site_packages_path in site_packages_paths:
+        site.addsitedir(site_packages_path)
+
+    sys.real_prefix = sys.prefix
+    sys.prefix = env_path
+    sys.exec_prefix = env_path
+
+    # Move the added items to the front of the path:
+    new_sys_path = []
+    for item in list(sys.path):
+        if item not in prev_sys_path:
+            new_sys_path.append(item)
+            sys.path.remove(item)
+    sys.path[:0] = new_sys_path