I installed both python 2.7 and 3.5, but python 3.5 is not working well

Question

In the terminal, I can start py -2successfully. Nonetheless,

C:\Users\user>py -3
Fatal Python error: Py_Initialize: unable to load the file system codec
  File "C:\Python27\lib\encodings\__init__.py", line 123
    raise CodecRegistryError,\
                            ^
SyntaxError: invalid syntax

Current thread 0x00004570 (most recent call first):

Answer 1

You can try setting the python path.

C:\Users\user>set PATH=C:\Program Files\Python 3.5;%PATH%
C:\Users\user>set PYTHONPATH=%PYTHONPATH%;C:\python_lib_path
C:\Users\user>python

Answer 2

I had the same problem. I found that my python 2.7 is x86 and my python 3.5 is x64, so I uninstalled both python 2 and 3, then reinstall python 2.7 and 3.5 as x64, then it works.

My installation applications are shown in the picture.

Answer 3

"PYTHONHOME". ( python27 x86 python36 x64)