There are two ways to import or use the code from other package:
import mypkg
from mypkg import *
There is a big difference between them.
from 是变量名拷贝运算，而非变量名的别名机制
For example: there is a package called mypkg
# mypgk.py
X = 99
def printer():
print (X)
如果我们在另一模块nested1.py内使用from导入两个变量名。
# nested1.py
from mypkg from X, printer # copy names
X = 1 # change my 'X' only
printer() # print mypkg's 'X' only which is still 99
% python nested1.py
99
BUT, 如果我们用import获得了整个模块，然后赋值某个点号运算的变量名，就会修改被导入模块中的变量的值。点号把python定向到了模块对象内的变量名，而不是导入者nested2.py的变量名。
# nested2.py
import mypkg # get module as a whole
mypkg.X = 1 # change mypkg's 'X'
mypkg.printer()
% python nested2.py
1
