点安装权限错误

我最近才通过自制软件重新安装了Python 2和Python 3，一切看起来都还不错。但是我在安装python之后pip3也进行了更新pip，然后，当尝试安装virtualenv时，出现以下错误：

~> pip install virtualenv Collecting virtualenv Downloading virtualenv-13.1.2-py2.py3-none-any.whl (1.7MB) 100% |

████████████████████████████████| 1.7MB 361kB/s Installing collected 
packages: virtualenv Exception: Traceback (most recent call last):
File "/usr/local/lib/python3.4/site-packages/pip/basecommand.py", line 211, in main status = self.run(options, args) 
File "/usr/local/lib/python3.4/site-packages/pip/commands/install.py", line 311, in run root=options.root_path, File "/usr/local/lib/python3.4/site-packages/pip/req/req_set.py", line 646, in install **kwargs 
File "/usr/local/lib/python3.4/site-packages/pip/req/req_install.py", line 803, in install self.move_wheel_files(self.source_dir, root=root) 
File "/usr/local/lib/python3.4/site-packages/pip/req/req_install.py", line 998, in move_wheel_files isolated=self.isolated, File "/usr/local/lib/python3.4/site-packages/pip/wheel.py", line 479, in move_wheel_files maker.make_multiple(['%s = %s' % kv for kv in console.items()]) File "/usr/local/lib/python3.4/site-packages/pip/_vendor/distlib/scripts.py", line 364, in make_multiple filenames.extend(self.make(specification, options)) 
File "/usr/local/lib/python3.4/site-packages/pip/_vendor/distlib/scripts.py", line 353, in make self._make_script(entry, filenames, options=options) 
File "/usr/local/lib/python3.4/site-packages/pip/_vendor/distlib/scripts.py", line 257, in _make_script self._write_script(scriptnames, shebang, script, filenames, ext) File "/usr/local/lib/python3.4/site-packages/pip/_vendor/distlib/scripts.py", line 231, in _write_script self._fileop.write_binary_file(outname, script_bytes) 
File "/usr/local/lib/python3.4/site-packages/pip/_vendor/distlib/util.py", line 388, in write_binary_file with open(path, 'wb') as f: 
PermissionError: [Errno 13] Permission denied: '/usr/local/bin/virtualenv'

pip freeze 然后似乎认为virtualenv已安装，但所有命令都不起作用。

有趣的是，如果我尝试卸载virtualenv，它似乎已将其安装到安装了Python 2版本brew的brew安装的Python 3上。

Uninstalling virtualenv-13.1.2:
  /usr/local/lib/python3.4/site-packages/__pycache__/virtualenv.cpython-34.pyc
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/DESCRIPTION.rst
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/METADATA
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/RECORD
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/WHEEL
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/entry_points.txt
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/metadata.json
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/pbr.json
  /usr/local/lib/python3.4/site-packages/virtualenv-13.1.2.dist-info/top_level.txt
  /usr/local/lib/python3.4/site-packages/virtualenv.py
  /usr/local/lib/python3.4/site-packages/virtualenv_support/__init__.py
  /usr/local/lib/python3.4/site-packages/virtualenv_support/__pycache__/__init__.cpython-34.pyc
  /usr/local/lib/python3.4/site-packages/virtualenv_support/argparse-1.3.0-py2.py3-none-any.whl
  /usr/local/lib/python3.4/site-packages/virtualenv_support/pip-7.1.2-py2.py3-none-any.whl
  /usr/local/lib/python3.4/site-packages/virtualenv_support/setuptools-18.2-py2.py3-none-any.whl
  /usr/local/lib/python3.4/site-packages/virtualenv_support/wheel-0.24.0-py2.py3-none-any.whl
Proceed (y/n)? 

点冻结给了我：

 ~> pip freeze
pbr==1.6.0
virtualenv==13.1.2
virtualenv-clone==0.2.6
wheel==0.24.0

因此virtualenv已安装，但由于某种原因无法正常工作。