为什么Pip会忽略冲突的依赖关系？

Question

如果我创建了一个虚拟包-这是/tmp/example_package/setup.py（请注意要求）：

from distutils.core import setup

setup(name='my_project',
      description="Just a test project",
      version="1.0",
      py_modules=['sample'],
      install_requires=['requests > 0.12'])

这是/tmp/example_package/sample.py：

import requests

def get_example():
    return requests.get("http://www.example.com")

现在，我创建一个virtualenv：

$ virtualenv /tmp/foobar --distribute -p python2.7
Running virtualenv with interpreter /usr/bin/python2.7
New python executable in /tmp/foobar/bin/python2.7
Also creating executable in /tmp/foobar/bin/python
Installing distribute.................................................................................................................................................................................................done.
Installing pip................done.
$ source /tmp/foobar/bin/activate

我创建了一个有冲突的需求的requirements.pip：

# this requires requests > 0.12:
file:///tmp/example_package

# but this conflicts:
requests==0.9.0

Pip高兴地安装了这个：

$ pip install -r requirements.pip                                                                                                                                                                       [18:40:10]
Unpacking ./example_package
  Running setup.py egg_info for package from file:///tmp/example_package

Downloading/unpacking requests==0.9.0 (from -r requirements.pip (line 3))
  Downloading requests-0.9.0.tar.gz (55Kb): 55Kb downloaded
  Running setup.py egg_info for package requests

Downloading/unpacking certifi>=0.0.4 (from requests==0.9.0->-r requirements.pip (line 3))
  Downloading certifi-0.0.8.tar.gz (118Kb): 118Kb downloaded
  Running setup.py egg_info for package certifi

Installing collected packages: requests, my-project, certifi
  Running setup.py install for requests

  Running setup.py install for my-project

  Running setup.py install for certifi

Successfully installed requests my-project certifi
Cleaning up...

为什么Pip允许这样做？我example_package无法使用，因为未满足其要求。

Answer 1

这是 Pip 的限制。需求文件胜过包的需求。请参阅https://github.com/pypa/pip/issues/775#issuecomment-12748095