python3  pip10以上

import pip
from pip._internal.utils.misc import get_installed_distributions
from subprocess import call 
for dist in get_installed_distributions():
    call("pip install --upgrade " + dist.project_name, shell=True)

pip 10以下

import pip
from subprocess import call
for dist in pip.get_installed_distributions():
    call("pip install --upgrade " + dist.project_name, shell=True)