摘要：
本机装有python2.7和python3.6，执行pip和pip2时没有问题，执行pip3时提示：
C:\Users\>pip3
Traceback (most recent call last):
File "e:\python36\lib\runpy.py", line , in _run_module_as_main
"__main__", mod_spec)
File "e:\python36\lib\runpy.py", line , in _run_code
exec(code, run_globals)
File "E:\Python36\Scripts\pip3.exe\__main__.py", line , in <module>
File "e:\python36\lib\re.py", line , in <module>
class RegexFlag(enum.IntFlag):
AttributeError: module 'enum' has no attribute 'IntFlag'
原因:
英文：This is likely caused by the package enum34. Since python 3.4 there's a standard library enum module, so you should uninstall enum34, which is no longer compatible with the enum in the standard library since enum.IntFlag was added in python 3.6.
中文：这可能是由enum34包引起的。因为python 3.4中有一个标准库枚举模块，所以您应该卸载enum34，它不再与标准库中的枚举兼容，因为枚举。IntFlag是在python 3.6中添加的。
解决办法：
pip uninstall enum34
#卸载enum34
卸载后执行pip3,成功，昨天整了大半天终于解决了
C:\Users>pip3 Usage:
pip3 <command> [options] Commands:
install Install packages.
download Download packages.
uninstall Uninstall packages.
freeze Output installed packages in requirements format.
list List installed packages.
show Show information about installed packages.
check Verify installed packages have compatible dependencies.
config Manage local and global configuration.
search Search PyPI for packages.
wheel Build wheels from your requirements.
hash Compute hashes of package archives.
completion A helper command used for command completion.
help Show help for commands.