Невозможно создать экземпляр virtualenv в python 2.7.5 из-за ошибки установки pip

Я пытаюсь следовать указаниям на веб-сайте установки Flask, но я столкнулся с ошибкой после того, как я использовал "sudo easy_install virtualenv" для установки виртуальной среды. Не уверен

Opals-MacBook-Pro:~ opalkale$ mkdir myproject
Opals-MacBook-Pro:~ opalkale$ cd myproject
Opals-MacBook-Pro:myproject opalkale$ virtualenv venv
New python executable in venv/bin/python
Installing setuptools, pip...
  Complete output from command /Users/opalkale/myproject/venv/bin/python -c "import sys, pip; pip...ll\"] + sys.argv[1:])" setuptools pip:
  Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/pip-1.5-py2.py3-none-any.whl/pip/__init__.py", line 9, in <module>
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/pip-1.5-py2.py3-none-any.whl/pip/log.py", line 8, in <module>
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 2696, in <module>
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 429, in __init__
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 443, in add_entry
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 1722, in find_in_zip
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 1298, in has_metadata
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 1614, in _has
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/pkg_resources.py", line 1488, in _zipinfo_name
AssertionError: /Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/EGG-INFO/PKG-INFO is not a subpath of /Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv_support/setuptools-2.0.2-py2.py3-none-any.whl/
----------------------------------------
...Installing setuptools, pip...done.
Traceback (most recent call last):
  File "/usr/local/bin/virtualenv", line 8, in <module>
load_entry_point('virtualenv==1.11', 'console_scripts', 'virtualenv')()
File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv.py", line 820, in main
symlink=options.symlink)
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv.py", line 988, in create_environment
install_wheel(to_install, py_executable, search_dirs)
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv.py", line 956, in install_wheel
'PIP_NO_INDEX': '1'
  File "/Library/Python/2.7/site-packages/virtualenv-1.11-py2.7.egg/virtualenv.py", line 898, in call_subprocess
% (cmd_desc, proc.returncode))
OSError: Command /Users/opalkale/myproject/venv/bin/python -c "import sys, pip; pip...ll\"] + sys.argv[1:])" setuptools pip failed with error code 1