如何在 iPython 中选择 Python 3.7 或 Python 3.8？

Question

My OS is Windows 7

I need to use TensorFlow with Keras in Python , but it doesn't work yet in Python 3.8 . So I've installed again Python 3.7 and his packages.

Inside the IDE PyCharm was easy. It just add another interpreter in settings and it works. So when I create a project I need to select the right interpreter.

I also use iPython to make small tests. I've searched in all Stackoverflow and I don't find any answer that works in 2020. I use iPython and not the Jupyter environment.

First, I've created the kernels, as iPython instructions said in its site.

python -m ipykernel install --user

It creates a json file in c:\\Users\\myname\\AppData\\Roaming\\jupyter\\kernels

After I use iPython -h and he told me to use kernel subcommand:

Subcommands are launched as `ipython cmd [args]`. For information on using
subcommand 'cmd', do: `ipython cmd -h`.

Feeling more motivated, I've tried the command iPython kernel -h . But I've got a very confusing text.

So I've tried to use the kernel option,

C:> iPython kernel

It gave me the following message:

To connect another client to this kernel, use:
    --existing kernel-3404.json

However, I'm not getting select the right kernel.

I try to use use my kernel file, but with no success.

Invalid argument: '--kernel.json'

So I'm lost, because in no place I've found a detailed instructions for kernel subcommand in line command options for iPython .

Answer 1

I've found a solution that solves my problem in Windows 7. I don't even need ipyKernet package.

I've started locating iPython.exe files in Python 3.7 and Python 3.8

c:\Users\myname\AppData\Local\Programs\Python\Python37\Scripts\ipython.exe 
c:\Users\myname\AppData\Local\Programs\Python\Python38\Scripts\ipython.exe 

So I've made the following script py.BAT and stored it in a folder inside the PATH environment variable (One can edit the PATH variable using Control Panel , Systems , Advanced system settings , environment variables ):

@echo off
cd\dropbox\python
if "%1"=="37" goto ip37
if "%1"=="38" goto ip38
if not "%1"== "" goto erro
:ip38
  c:\Users\myname\AppData\Local\Programs\Python\Python38\Scripts\ipython
  goto fim
:ip37
  c:\Users\myname\AppData\Local\Programs\Python\Python37\Scripts\ipython
  goto fim
:erro
  echo Syntax: py 37   - iPython 3.7 
  echo         py 38   - iPython 3.8
  echo         py      - iPython 3.8
:fim

Now it's a piece of cake:

If I want to run iPython over Python 3.7

py 37

If I what to run iPython over Python 3.8

py  

or

py 38

Of course I've checked Python version in each iPython session:

import sys
print(sys.version)

The messages was

3.8.1 (tags/v3.8.1:1b293b6, Dec 18 2019, 23:11:46) [MSC v.1916 64 bit (AMD64)]

or

3.7.6 (tags/v3.7.6:43364a7ae0, Dec 19 2019, 00:42:30)[MSC v.1916 64 bit (AMD64)]

Any other param

py 40 # e.g.

results in

Syntax: py 37   - iPython 3.7
        py 38   - iPython 3.8
        py      - iPython 3.8

Internal references in Python don't use PATH environment variables in general, but when one uses an utility in the shell as pip , has a problem because if you write pip in the shell, it searchs the first executable in the order of the string content in the PATH variable, generally the last Python version.

So one has to make a copy in the old Python version that utility in the same folder (please not rename the original file) with another name (Eg: pip.exe to pi.exe )

Other solution would be temporarily change the path environment variable inside PY.BAT and any other, if necessary. I haven't done it yet because everything is fine so far.