jupyter notebook 配置多anaconda/python内核

问题描述：

在anaconda创建了虚拟环境my_tensorflow，并且安装了sklearn。

进入虚拟环境，可以成功导入sklearn：

python

>> import sklearn

但是，在 jupyter notebook 却无法导入，ImportError: No module named 'sklearn.__check_build._check_build'：

---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
D:\MY\Anaconda3\lib\site-packages\sklearn\__check_build\__init__.py in <module>
     43 try:
---> 44     from ._check_build import check_build  # noqa
     45 except ImportError as e:

ModuleNotFoundError: No module named 'sklearn.__check_build._check_build'

During handling of the above exception, another exception occurred:

ImportError                               Traceback (most recent call last)
<ipython-input-2-47b27fd5bde7> in <module>
      3 import matplotlib.pyplot as plt
      4 # from testCases import *
----> 5 import sklearn
      6 import sklearn.datasets
      7 import sklearn.linear_model

D:\MY\Anaconda3\lib\site-packages\sklearn\__init__.py in <module>
    131     # process, as it may not be compiled yet
    132 else:
--> 133     from . import __check_build
    134     from .base import clone
    135     __check_build  # avoid flakes unused variable error

D:\MY\Anaconda3\lib\site-packages\sklearn\__check_build\__init__.py in <module>
     44     from ._check_build import check_build  # noqa
     45 except ImportError as e:
---> 46     raise_build_error(e)

D:\MY\Anaconda3\lib\site-packages\sklearn\__check_build\__init__.py in raise_build_error(e)
     39 to build the package before using it: run `python setup.py install` or
     40 `make` in the source directory.
---> 41 %s""" % (e, local_dir, ''.join(dir_content).strip(), msg))
     42 
     43 try:

ImportError: No module named 'sklearn.__check_build._check_build'
___________________________________________________________________________
Contents of D:\MY\Anaconda3\lib\site-packages\sklearn\__check_build:
setup.py                  _check_build.cp37-win_amd64.pyd__init__.py
__pycache__
___________________________________________________________________________
It seems that scikit-learn has not been built correctly.

If you have installed scikit-learn from source, please do not forget
to build the package before using it: run `python setup.py install` or
`make` in the source directory.

If you have used an installer, please check that it is suited for your
Python version, your operating system and your platform.

在 jupyter notebook 中输入：

import sys
sys.excutable

我们发现，显示的python解释器是默认的解释器，并不是虚拟环境的解释器：

这下问题就清楚了，sklearn 安装在虚拟环境中，用默认环境的解释器当然会出错。

解决方法：

我们需要将虚拟环境的解释器添加到 jupyter notebook 中，在运行 jupyter notebook 文件的时候选择这个解释器就行了。

# 进入目标虚拟环境
conda activate env_name

# 安装 ipykernel
pip install ipykernel

# 通过 ipykernel 为 jupyter notebook 添加内核
python -m ipykernel install --name env_name

# 退出虚拟环境
deactivate

# 启动 jupyter notebook
jupyter notebook

这时，在 kernel -> change kernel 一栏里就可以选择我们新添加的环境了：

我们可以看到 C:\ProgramData\jupyter\kernels 下多了刚刚添加的 kernel：

里面的 kernel.json 文件里写入了刚刚添加的执行器：