update windows build to Python 3.7

Lib/lib2to3/fixes/fix_ws_comma.py

@@ -0,0 +1,39 @@
+"""Fixer that changes 'a ,b' into 'a, b'.
+
+This also changes '{a :b}' into '{a: b}', but does not touch other
+uses of colons.  It does not touch other uses of whitespace.
+
+"""
+
+from .. import pytree
+from ..pgen2 import token
+from .. import fixer_base
+
+class FixWsComma(fixer_base.BaseFix):
+
+    explicit = True # The user must ask for this fixers
+
+    PATTERN = """
+    any<(not(',') any)+ ',' ((not(',') any)+ ',')* [not(',') any]>
+    """
+
+    COMMA = pytree.Leaf(token.COMMA, ",")
+    COLON = pytree.Leaf(token.COLON, ":")
+    SEPS = (COMMA, COLON)
+
+    def transform(self, node, results):
+        new = node.clone()
+        comma = False
+        for child in new.children:
+            if child in self.SEPS:
+                prefix = child.prefix
+                if prefix.isspace() and "\n" not in prefix:
+                    child.prefix = ""
+                comma = True
+            else:
+                if comma:
+                    prefix = child.prefix
+                    if not prefix:
+                        child.prefix = " "
+                comma = False
+        return new