fix #432 (#435)

setup.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 import subprocess
-
+import os
 from setuptools import setup, find_packages
 from setuptools.command.develop import develop
 from setuptools.command.install import install
@@ -32,8 +32,12 @@ def run(self):
 
 # comment if preparing PyPI package
 version = '1.7'
-sha = subprocess.check_output(['git', 'rev-parse', 'HEAD']).decode('ascii').strip()
-version_git = version + '+' + sha[:7]
+
+if os.path.exists('.git'):
+    sha = subprocess.check_output(['git', 'rev-parse', 'HEAD']).decode('ascii').strip()
+    version_git = version + '+' + sha[:7]
+else:
+    version_git = version
 
 with open('tensorboardX/__init__.py', 'a') as f:
     f.write('\n__version__ = "{}"\n'.format(version_git))