使用pip install安装软件包时出现问题

Question

我需要安装pyspark。它依赖于pypandoc。所以我先做pip install pypandoc，然后做pip install pyspark，一切看起来都很好。但是，根据某些要求，我需要使用requirements.txt文件安装依赖项。因此，我将pypandoc和pyspark都放在了requirements.txt文件中，然后我做了pip install -r requirements.txt（pypandoc首先出现在文件中，然后是pyspark），但是这次是安装文件出现以下错误

 Complete output from command python setup.py egg_info:
Could not import pypandoc - required to package PySpark
Download error on https://pypi.org/simple/pypandoc/: [Errno 97] Address family not supported by protocol -- Some packages may not be found!
Couldn't find index page for 'pypandoc' (maybe misspelled?)
Download error on https://pypi.org/simple/: [Errno 97] Address family not supported by protocol -- Some packages may not be found!
No local packages or working download links found for pypandoc
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/tmp/pip-install-6vmbjchu/pyspark/setup.py", line 224, in <module>
    'Programming Language :: Python :: Implementation :: PyPy']
  File "/usr/local/lib/python3.6/site-packages/setuptools/__init__.py", line 144, in setup
    _install_setup_requires(attrs)
  File "/usr/local/lib/python3.6/site-packages/setuptools/__init__.py", line 139, in _install_setup_requires
    dist.fetch_build_eggs(dist.setup_requires)
  File "/usr/local/lib/python3.6/site-packages/setuptools/dist.py", line 724, in fetch_build_eggs
    replace_conflicting=True,
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 782, in resolve
    replace_conflicting=replace_conflicting
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1065, in best_match
    return self.obtain(req, installer)
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1077, in obtain
    return installer(requirement)
  File "/usr/local/lib/python3.6/site-packages/setuptools/dist.py", line 791, in fetch_build_egg
    return cmd.easy_install(req)
  File "/usr/local/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 673, in easy_install
    raise DistutilsError(msg)
distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('pypandoc')

因此，当我以此方式执行操作时，尝试安装pypandoc时pyspark的安装不正确。我该如何解决这个问题？