从命令行(Mac OS),当我执行 'echo $PYTHONPATH' 我得到:
> /opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
如果我然后输入 Python 解释器并执行以下操作:
>>> import os
>>> os.environ['PYTHONPATH']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/UserDict.py", line 23, in __getitem__
raise KeyError(key)
KeyError: 'PYTHONPATH'
为什么会发生这种情况?