将 pip 链接到 python 3.7 时出现问题。 pip 和 pip3 均已安装，但链接到 Python 2.7。
我尝试重新安装Python3，然后pip，但没有任何进展。
我收到以下消息：
软件包 python3-pip 不可用，但被另一个软件包引用。
这可能意味着该软件包丢失、已过时或只能从其他来源获得
$ python --version
Python 3.7.4
$ pip -V
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
warnings.warn(warning, RequestsDependencyWarning)
pip 19.2.1 from /usr/local/lib/python2.7/dist-packages/pip (python 2.7)
$ pip3 -V
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
warnings.warn(warning, RequestsDependencyWarning)
pip 19.2.1 from /usr/local/lib/python2.7/dist-packages/pip (python 2.7)
$ sudo apt-get install python3-pip
[sudo] password for TarikDev:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package python3-pip is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'python3-pip' has no installation candidate