python之pkg_resources.DistributionNotFound : The 'pip==1.5.4' distribution was not found and is required by the application

在 Ubuntu 和 Python 2.7.6 上工作，我正在尝试使用 pip。当我只输入 pip 然后回车时，我得到:

File "/usr/local/bin/pip", line 5, in <module> 
  from pkg_resources import load_entry_point 
File "build/bdist.linux-x86_64/egg/pkg_resources/__init__.py", line 3095, in  <module> 
File "build/bdist.linux-x86_64/egg/pkg_resources/__init__.py", line 3081, in _call_aside 
File "build/bdist.linux-x86_64/egg/pkg_resources/__init__.py", line 3108, in _initialize_master_working_set 
File "build/bdist.linux-x86_64/egg/pkg_resources/__init__.py", line 660, in _build_master 
File "build/bdist.linux-x86_64/egg/pkg_resources/__init__.py", line 673, in _build_from_requirements 
File "build/bdist.linux-x86_64/egg/pkg_resources/__init__.py", line 846, in resolve 
pkg_resources.DistributionNotFound: The 'pip==1.5.4' distribution was not found and is required by the application