if no cmake generator is set use same logic as cmake to find default buid…

if no cmake generator is set use same logic as cmake to find default buid generator but use Win64 if the build is for 64bit Python

setup.py

@@ -121,6 +121,126 @@ def _get_options():
 
 options, cmake_config, cmake_path, cmake_extra, generator_set = _get_options()
 
+
+def reg_value(rk, rname):
+    """enumerate the subkeys in a registry key
+    :param rk: root key in registry
+    :param rname: name of the value we are interested in
+    """
+    try:
+        import _winreg as winreg
+    except ImportError:
+        # noinspection PyUnresolvedReferences
+        import winreg
+
+    count = 0
+    try:
+        while True:
+            name, value, _ = winreg.EnumValue(rk, count)
+            if rname == name:
+                return value
+            count += 1
+    except OSError:
+        pass
+
+    return None
+
+
+def enum_reg_key(rk):
+    """enumerate the subkeys in a registry key
+    :param rk: root key in registry
+    """
+    try:
+        import _winreg as winreg
+    except ImportError:
+        # noinspection PyUnresolvedReferences
+        import winreg
+
+    sub_keys = []
+    count = 0
+    try:
+        while True:
+            name = winreg.EnumKey(rk, count)
+            sub_keys.append(name)
+            count += 1
+    except OSError:
+        pass
+
+    return sub_keys
+
+
+def get_msvc_win64_generator():
+    """find the default MSVC generator but Win64
+    This logic closely matches cmake's resolution for default build generator.
+    Only we select the Win64 version of it.
+    """
+    try:
+        import _winreg as winreg
+    except ImportError:
+        # noinspection PyUnresolvedReferences
+        import winreg
+
+    known_vs = {
+        "6.0": "Visual Studio 6",
+        "7.0": "Visual Studio 7",
+        "7.1": "Visual Studio 7 .NET 2003",
+        "8.0": "Visual Studio 8 2005",
+        "9.0": "Visual Studio 9 2008",
+        "10.0": "Visual Studio 10 2010",
+        "11.0": "Visual Studio 11 2012",
+        "12.0": "Visual Studio 12 2013",
+        "14.0": "Visual Studio 14 2015",
+    }
+
+    newest_vs = None
+    newest_ver = 0
+
+    platform_arch = platform.architecture()[0]
+    sam = winreg.KEY_WOW64_32KEY + winreg.KEY_READ if '64' in platform_arch else winreg.KEY_READ
+    for vs in ['VisualStudio\\', 'VCExpress\\', 'WDExpress\\']:
+        vs_key = "SOFTWARE\\Microsoft\\{vs}\\".format(vs=vs)
+        try:
+            root_key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, vs_key, 0, sam)
+        except OSError:
+            continue
+        try:
+            sub_keys = enum_reg_key(root_key)
+        except OSError:
+            sub_keys = []
+        winreg.CloseKey(root_key)
+        if not sub_keys:
+            continue
+
+        # look to see if we have InstallDir
+        for sub_key in sub_keys:
+            try:
+                root_key = winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, vs_key + sub_key, 0, sam)
+            except OSError:
+                continue
+            ins_dir = reg_value(root_key, 'InstallDir')
+            winreg.CloseKey(root_key)
+
+            if not ins_dir:
+                continue
+
+            gen_name = known_vs.get(sub_key)
+            if gen_name is None:
+                # if it looks like a version number
+                try:
+                    ver = float(sub_key)
+                except ValueError:
+                    continue
+                gen_name = 'Visual Studio %d' % int(ver)
+            else:
+                ver = float(sub_key)
+
+            if ver > newest_ver:
+                newest_vs = gen_name
+
+    if newest_vs:
+        return ['-G', newest_vs + ' Win64']
+    return []
+
 try:
     from Queue import Queue, Empty
 except ImportError:
@@ -335,6 +455,12 @@ class build(_build):
             cmake_extra_arch += ['-DPYTHON3=yes']
 
         if platform_arch == '64bit' and sys.platform == "win32":
+            # 64bit build on Windows
+
+            if not generator_set:
+                # see if we can deduce the 64bit default generator
+                cmake_extra_arch += get_msvc_win64_generator()
+
             # help cmake to find Python library in 64bit Python in Windows
             #  because cmake is 32bit and cannot find PYTHON_LIBRARY from registry.
             inc_dir = get_python_inc()