python3 安装scrapy Exception: Traceback (most recent call last): File "/usr/lib/python3/dist-packages/pip/req/req_install.py", line 1006, in check_if_exists解决方法

错误代码：

Exception:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/pip/req/req_install.py", line 1006, in check_if_exists
    self.satisfied_by = pkg_resources.get_distribution(str(no_marker))
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 535, in get_distribution
    dist = get_provider(dist)
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 415, in get_provider
    return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
  File "/usr/share/python-wheels/pkg_resources-0.0.0-py2.py3-none-any.whl/pkg_resources/__init__.py", line 695, in find
    raise VersionConflict(dist, req)
pkg_resources.VersionConflict: (cryptography 1.2.3 (/usr/lib/python3/dist-packages), Requirement.parse('cryptography>=1.3'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/pip/basecommand.py", line 209, in main
    status = self.run(options, args)
  File "/usr/lib/python3/dist-packages/pip/commands/install.py", line 317, in run
    requirement_set.prepare_files(finder)
  File "/usr/lib/python3/dist-packages/pip/req/req_set.py", line 360, in prepare_files
    ignore_dependencies=self.ignore_dependencies))
  File "/usr/lib/python3/dist-packages/pip/req/req_set.py", line 448, in _prepare_file
    req_to_install, finder)
  File "/usr/lib/python3/dist-packages/pip/req/req_set.py", line 387, in _check_skip_installed
    req_to_install.check_if_exists()
  File "/usr/lib/python3/dist-packages/pip/req/req_install.py", line 1011, in check_if_exists
    self.req.project_name
AttributeError: 'Requirement' object has no attribute 'project_name'

解决方法：安装全所需库文件即可：

sudo apt-get install build-essential
sudo apt-get install python3-dev
sudo apt-get install libxml2-de;
sudo apt-get install libxslt1-dev
sudo apt-get install libssl-dev
apt-get install -y libffi-dev
pip3 install Twisted
pip3 install w3lib
pip3 install lxm