python - airflow安装为什么会报错？

用pip install airflow报错

[root@data pip-8.1.2]# python --version
Python 2.6.6

[root@data pip-8.1.2]# pip --version
pip 8.1.2 from /usr/lib/python2.6/site-packages/pip-8.1.2-py2.6.egg (python 2.6)

 build/lib/markdown/__init__.py:259: DeprecationWarning: Using short names for Markdown's builtin extensions is deprecated. Use the full path to the extension with Python's dot notation (eg: "markdown.extensions.smarty" instead of "smarty"). The current behavior will raise an error in version 2.7. See the Release Notes for Python-Markdown version 2.6 for more info.
      DeprecationWarning)
    creating build/docs
    copying docs/release-2.3.txt -> build/docs
    Converting docs/release-2.3.txt -> build/docs/release-2.3.html
    Traceback (most recent call last):
      File "", line 1, in 
      File "/tmp/pip-build-WzDeTI/markdown/setup.py", line 270, in 
        'Topic :: Text Processing :: Markup :: HTML'
      File "/usr/lib64/python2.6/distutils/core.py", line 152, in setup
        dist.run_commands()
      File "/usr/lib64/python2.6/distutils/dist.py", line 975, in run_commands
        self.run_command(cmd)
      File "/usr/lib64/python2.6/distutils/dist.py", line 995, in run_command
        cmd_obj.run()
      File "build/bdist.linux-x86_64/egg/setuptools/command/install.py", line 61, in run
      File "/usr/lib64/python2.6/distutils/command/install.py", line 577, in run
        self.run_command('build')
      File "/usr/lib64/python2.6/distutils/cmd.py", line 333, in run_command
        self.distribution.run_command(command)
      File "/usr/lib64/python2.6/distutils/dist.py", line 995, in run_command
        cmd_obj.run()
      File "/usr/lib64/python2.6/distutils/command/build.py", line 134, in run
        self.run_command(cmd_name)
      File "/usr/lib64/python2.6/distutils/cmd.py", line 333, in run_command
        self.distribution.run_command(command)
      File "/usr/lib64/python2.6/distutils/dist.py", line 995, in run_command
        cmd_obj.run()
      File "/tmp/pip-build-WzDeTI/markdown/setup.py", line 184, in run
        out = template % self._get_context(src, outfile)
      File "/tmp/pip-build-WzDeTI/markdown/setup.py", line 116, in _get_context
        c['body'] = self.md.convert(src)
      File "build/lib/markdown/__init__.py", line 375, in convert
        newRoot = treeprocessor.run(root)
      File "build/lib/markdown/extensions/toc.py", line 229, in run
        for el in doc.iter():
    AttributeError: iter
    
    ----------------------------------------
Command "/usr/bin/python -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-WzDeTI/markdown/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-__TaTb-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-build-WzDeTI/markdown/