python导包错误 ImportError: cannot i

1. 开发工具pycharm
2. 运行方式

• pycharm右键运行
• python命令执行

3. 项目目录结构

   
   cloud_platform
4. 代码

import os
import sys

from test import a
a.test()

5. 问题

Traceback (most recent call last):
  File "monitor_yarn/aa.py", line 1, in <module>
    from test import a
ImportError: cannot import name a

• 在pycharm中右键运行没问题，但是去服务器直接用python命令去直接执行就会报上面的错误
• 这是因为在用python命令执行时test包默认没有引入到sys.path中
• 继续看代码

import os
import sys

for i in sys.path:
    print i
from test import a
a.test()

#输出
/Users/wangtaiyang/PycharmProjects/cloud_platform_script/monitor_yarn
/Library/Frameworks/Python.framework/Versions/2.7/lib/python27.zip
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-old
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/yarn_api_client-0.3.1-py2.7.egg

• 看上面打印信息可以看到并没有test这个包的路径，而用pycharm右键运行项目时，打印：

/Users/wangtaiyang/PycharmProjects/cloud_platform_script/monitor_yarn
/Users/wangtaiyang/PycharmProjects/cloud_platform_script
/Library/Frameworks/Python.framework/Versions/2.7/lib/python27.zip
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-old
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/yarn_api_client-0.3.1-py2.7.egg
/Applications/PyCharm.app/Contents/helpers/pycharm_matplotlib_backend
test

• 可以看到是有当前运行的文件的路径 And 这个项目的根路径

6. 解决方法

• 三种解决方法
  1. 在/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages下添加一个xx.pth，xx是要导入的模块名，然后写上本地项目路径，这种方法在换一个环境用时太麻烦，不推荐
  2. 将包的路径添加到sys.path中

#sys.py文件中，sys.path就是一个列表
path = [
    '/Applications/PyCharm.app/Contents/helpers',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python27.zip',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-old',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload',
    '/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages',
]

#在自己代码中向path列表中添加要导入的包的路径
os.sys.path.append('/Users/wangtaiyang/PycharmProjects/cloud_platform_script/test')

这种方式每个文件都需要添加，也很麻烦

3. 添加PYTHONPATH环境变量(推荐)

export PYTHONPATH=/Users/wangtaiyang/PycharmProjects/cloud_platform_script/monitor_yarn

• 这种方式也是我最喜欢的方式，换了执行环境，只需配置一条环境变量而已，比起上面两种方式要方便的多

总结

pycharm中运行代码，它自动就为你设置好了项目的路径到sys.path中，而我们的项目往往要到服务器运行，而在用python命令执行时，项目的路径需要我们自己配置