pip install python-esl 时会报错：
“error: command ‘swig’ failed with exit status 1”

报错原因是 因为 swig 软件未正确安装，当然对swig的版本也是有要求的，目前测试以下版本没有问题：

swig==3.0.63
python-ESL==1.4.18

(app-root) pip install swig==3.0.6
Collecting swig==3.0.6
  Downloading swig-3.0.6-py2.py3-none-manylinux_2_5_x86_64.manylinux1_x86_64.whl (3.4 MB)
     |████████████████████████████████| 3.4 MB 42 kB/s            
Installing collected packages: swig
  Attempting uninstall: swig
    Found existing installation: swig 4.1.1
    Uninstalling swig-4.1.1:
      Successfully uninstalled swig-4.1.1
Successfully installed swig-3.0.6
(app-root) pip install python-ESL==1.4.18
Collecting python-ESL==1.4.18
  Downloading python-ESL-1.4.18.tar.gz (40 kB)
     |████████████████████████████████| 40 kB 160 kB/s            
  Preparing metadata (setup.py) ... done
Building wheels for collected packages: python-ESL
  Building wheel for python-ESL (setup.py) ... done
  Created wheel for python-ESL: filename=python_ESL-1.4.18-cp36-cp36m-linux_x86_64.whl size=185967 sha256=a5a7a41dab808869f907be85d9797fde8734c8af345166258858499a97e4b7c2
  Stored in directory: /tmp/pip-ephem-wheel-cache-1c7qzocb/wheels/60/03/8f/db19b3b185566fd3be60428c4ba8af4ef0486cbeba7ef9004c
Successfully built python-ESL
Installing collected packages: python-ESL
Successfully installed python-ESL-1.4.18