尝试安装scikit-learn时遇到错误：
$ pip3 install scikit-learn
-bash: pip3: command not found here
$ pip install scikit-learn
-bash: pip3.4: command not found
我该如何解决这个问题？我已经尝试卸载pip并通过python3重新安装它，但似乎没有任何效果。
但是，Pip3似乎仍然安装在我的机器上：
$ locate pip3
/opt/local/var/macports/sources/rsync.macports.org/release/tarballs/ports/python/py-pip/files/pip33
/opt/local/var/macports/sources/rsync.macports.org/release/tarballs/ports/python/py-pip/files/pip34
/usr/local/Cellar/python3/3.4.3/bin/pip3
/usr/local/Cellar/python3/3.4.3/bin/pip3.4
/usr/local/Cellar/python3/3.5.0/bin/pip3
/usr/local/Cellar/python3/3.5.0/bin/pip3.5
/usr/local/Cellar/python3/3.5.1/bin/pip3
/usr/local/Cellar/python3/3.5.1/bin/pip3.5
/usr/local/bin/pip3
/usr/local/bin/pip3.5