为什么我的python3pip模块安装在两个不同的目录中

Question

我不明白为什么使用相同的命令，一些python3pip模块被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你说得对，我刚刚发现我的系统上同时安装了python-requests和python3-requestsUbuntu软件包。 但是，我无法卸载它们，因为许多其他ubuntu包都依赖于它们。你知道吗

如果有人知道原因，请告知：-）

EDIT2：请注意，我不想/usr/local/bin/pip3接触系统/usr/lib/python3/dist-packages目录。你知道吗

我只是想确保通过/usr/local/bin/pip3安装的软件包始终安装到/usr/local/lib/python3.6或/usr/local/lib/python3.