我不明白为什么使用相同的命令，一些 python3 pip 模块已安装在两个不同的位置：
$ /usr/local/bin/pip3 -V
pip 19.1 from /usr/local/lib/python3.6/dist-packages/pip (python 3.6)
$ sudo -H /usr/local/bin/pip3 install pychromecast | grep /usr/local/lib/python
Requirement already satisfied: pychromecast in /usr/local/lib/python3.6/dist-packages (3.2.1)
Requirement already satisfied: protobuf>=3.0.0 in /usr/local/lib/python3.6/dist-packages (from pychromecast) (3.7.1)
Requirement already satisfied: zeroconf>=0.17.7 in /usr/local/lib/python3.6/dist-packages (from pychromecast) (0.22.0)
Requirement already satisfied: casttube>=0.2.0 in /usr/local/lib/python3.6/dist-packages (from pychromecast) (0.2.0)
Requirement already satisfied: setuptools in /usr/local/lib/python3.6/dist-packages (from protobuf>=3.0.0->pychromecast) (41.0.1)
Requirement already satisfied: six>=1.9 in /usr/local/lib/python3.6/dist-packages (from protobuf>=3.0.0->pychromecast) (1.12.0)
Requirement already satisfied: ifaddr in /usr/local/lib/python3.6/dist-packages (from zeroconf>=0.17.7->pychromecast) (0.1.6)
$ sudo -H /usr/local/bin/pip3 install pychromecast | grep /usr/lib/python
Requirement already satisfied: requests>=2.0 in /usr/lib/python3/dist-packages (from pychromecast) (2.2.1)
EDIT0：我的sys.path：
$ /usr/local/bin/python3 -c "import sys;print(sys.path)"
['', '/usr/lib/python36.zip', '/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload', '/usr/local/lib/python3.6/dist-packages', '/usr/lib/python3/dist-packages']
EDIT1：@furas 你是对的，我刚刚发现我的系统上都安装了 Ubuntupython-requests和Ubuntu 软件包。python3-requests但是，我无法卸载它们，因为许多其他 ubuntu 软件包都依赖于它们。
如果有人明白为什么，请告诉我:-)
EDIT2：请注意，我不想/usr/local/bin/pip3触摸系统/usr/lib/python3/dist-packages目录。
我只是想确保我安装的软件包/usr/local/bin/pip3将始终安装到/usr/local/lib/python3.6or/usr/local/lib/python3.