一般來說，電腦裡會有許多版本的python，由下述方式可以知道有那些版本
pi@raspb2:~/Downloads $ sudo ls /usr/bin/python*
sudo: unable to resolve host raspb2
/usr/bin/python /usr/bin/python2.7-config /usr/bin/python3.5 /usr/bin/python3.5m-config /usr/bin/python3m-config
/usr/bin/python2 /usr/bin/python2-config /usr/bin/python3.5-config /usr/bin/python3-config /usr/bin/python-config
/usr/bin/python2.7 /usr/bin/python3 /usr/bin/python3.5m /usr/bin/python3m
而目前的版本為何呢?
pi@raspb2:~/Downloads $ python --version
Python 2.7.13
利用alias來變更預設版本，並且重新login .bashrc，即可變更預設的版本。
pi@raspb2:~/Downloads $ alias python="/usr/bin/python3.5"
pi@raspb2:~/Downloads $ . ~/.bashrc
pi@raspb2:~/Downloads $ python --version
Python 3.5.3