错误的错误信息

Question

我的笔记本电脑上装有 ubuntu 16.04，以及 python 2.7。在某个时候，我修改了我的，PYTHONPATH以便它可以与一起使用tensorflow。但是，如果我ls-在终端中输入，那么我收到的错误是

Traceback (most recent call last):
  File "/usr/lib/command-not-found", line 23, in <module>
    import gettext
  File "/usr/lib/python3.5/gettext.py", line 49, in <module>
    import locale, copy, io, os, re, struct, sys
  File "/usr/lib/python3.5/locale.py", line 16, in <module>
    import re
  File "/usr/lib/python3.5/re.py", line 335, in <module>
    import copyreg
  File "/home/<username>/.local/lib/python2.7/site-packages/copyreg/__init__.py", line 7, in <module>
    raise ImportError('This package should not be accessible on Python 3. '
ImportError: This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 53, in apport_excepthook
    if not enabled():
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 24, in enabled
    import re
  File "/usr/lib/python3.5/re.py", line 335, in <module>
    import copyreg
  File "/home/<username>/.local/lib/python2.7/site-packages/copyreg/__init__.py", line 7, in <module>
    raise ImportError('This package should not be accessible on Python 3. '
ImportError: This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.

Original exception was:
Traceback (most recent call last):
  File "/usr/lib/command-not-found", line 23, in <module>
    import gettext
  File "/usr/lib/python3.5/gettext.py", line 49, in <module>
    import locale, copy, io, os, re, struct, sys
  File "/usr/lib/python3.5/locale.py", line 16, in <module>
    import re
  File "/usr/lib/python3.5/re.py", line 335, in <module>
    import copyreg
  File "/home/<username>/.local/lib/python2.7/site-packages/copyreg/__init__.py", line 7, in <module>
    raise ImportError('This package should not be accessible on Python 3. '
ImportError: This package should not be accessible on Python 3. Either you are trying to run from the python-future src folder or your installation of python-future is corrupted.

它应该是

bash: ls-: command not found

我是一个很挑剔的人，所以这有点困扰我。谢谢！