it's more pythonic to use 'is not None' in python files

Author: Guanqun Lu

src/bootstrap/bootstrap.py

@@ -668,7 +668,7 @@ def check_submodule(self, module, slow_submodules):
     def update_submodule(self, module, checked_out, recorded_submodules):
         module_path = os.path.join(self.rust_root, module)
 
-        if checked_out != None:
+        if checked_out is not None:
             default_encoding = sys.getdefaultencoding()
             checked_out = checked_out.communicate()[0].decode(default_encoding).strip()
             if recorded_submodules[module] == checked_out:

src/libcore/unicode/printable.py

@@ -60,7 +60,7 @@ def get_codepoints(f):
         yield Codepoint(codepoint, class_)
         prev_codepoint = codepoint
 
-    if class_first != None:
+    if class_first is not None:
         raise ValueError("Missing Last after First")
 
     for c in range(prev_codepoint + 1, NUM_CODEPOINTS):