C:\Windows\system32>pip install git+https://github.com/pythonnet/pythonnet
Collecting git+https://github.com/pythonnet/pythonnet
  Cloning https://github.com/pythonnet/pythonnet to c:\users\denis~1.akh\appdata\local\temp\pip-so1nbo-build
  Requirement already satisfied (use --upgrade to upgrade): pythonnet==2.4.0.dev0 from git+https://github.com/pythonnet/pythonnet in c:\python\python27-32\lib\site-packages

C:\Windows\system32>pip install git+https://github.com/pythonnet/pythonnet -U
Collecting git+https://github.com/pythonnet/pythonnet
  Cloning https://github.com/pythonnet/pythonnet to c:\users\denis~1.akh\appdata\local\temp\pip-ytahwe-build
Installing collected packages: pythonnet
  Found existing installation: pythonnet 2.4.0.dev0
    Uninstalling pythonnet-2.4.0.dev0:
      Successfully uninstalled pythonnet-2.4.0.dev0
  Running setup.py install for pythonnet ... error
    Complete output from command c:\python\python27-32\python.exe -u -c "import setuptools, tokenize;__file__='c:\\users\\denis~1.akh\\appdata\\local\\temp\\pip-ytahwe-build\\setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record c:\users\denis~1.akh\appdata\local\temp\pip-3dupcl-record\install-record.txt --single-version-externally-managed --compile:
    usage: -c [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
       or: -c --help [cmd1 cmd2 ...]
       or: -c --help-commands
       or: -c cmd --help

    error: option --single-version-externally-managed not recognized

    ----------------------------------------
  Rolling back uninstall of pythonnet
Command "c:\python\python27-32\python.exe -u -c "import setuptools, tokenize;__file__='c:\\users\\denis~1.akh\\appdata\\local\\temp\\pip-ytahwe-build\\setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record c:\users\denis~1.akh\appdata\local\temp\pip-3dupcl-record\install-record.txt --single-version-externally-managed --compile" failed with error code 1 in c:\users\denis~1.akh\appdata\local\temp\pip-ytahwe-build\