When I teach Python I keep telling my students to avoid importing using *, but it isn't always easy as there are many examples on the Internet, some even in official documentation, using code like: 

from tkinter import *

Instead of that it would be better to write: 

import tkinter as tk

But why?

Automatic function overwriting

Let's say you have this code: 

from Amodule import *
from Bmodule import *

and you use the function calc from Amodule.

Then you upgrade Bmodule (an external module) and it starts to also provide a function called calc. Maybe it is a helper function of Bmodule so it is not even documented.

Suddenly your code starts to use the function calc provided by Bmodule.

Python does not even complain, but this is not what you wanted.

So in general it is better to avoid this feature of Python.

In general it is better to be explicit about what you are importing than implicit.

Oh, and in case you say "but I only use * for one module" here is the same example for you: 

from Amodule import calc
from Bmodule import *

In this example your code will still break if Bmodule starts to have a function called calc. Which, by the way can happen even if Bmodule only imports a function called calc.

Tk - tkinter

Back to the tkinter example you might have some code like this: 

from tkinter import *

and then your code uses keywords such as Tk, Menu, Frame, Label, Button.

It is better to explicitly import whatever you need: 

import tkinter as tk

and then use the objects of tkinter with their full names: 

tk.Tk   instead of Tk
tk.Menu instead of Menu