为什么命名/通配符导入会/如何影响参数？

Question

So... I'm tinkering with some basic python/tkinter programs, and translating the code from python 2.x in the book I'm reading, to 3.x to make sure I understand everything. I was also attempting to write the code with 'proper' named imports instead of wild card import ie from tkinter import * but its not working out so well...

What has me baffled at the moment is this: the original code does a wildcard import of tkinter, and seems to be able to 'get away with' not using quotes around parameter variables like sticky=W , while if I do a named import I have to use quotes around the 'W' or I get an error Unresolved reference 'W' .

Example code (wildcard import):

from tkinter import *
root = Tk()

Label(root, text="Username").grid(row=0, sticky=W)
Label(root, text="Password").grid(row=1, sticky=W)
Entry(root).grid(row=0, column=1, sticky=E)
Entry(root).grid(row=1, column=1, sticky=E)
Button(root, text="Login").grid(row=2, column=1, sticky=E)

root.mainloop()

Named import:

import tkinter as tk

root = tk.Tk()

tk.Label(root, text="Username").grid(row=0, sticky='W')
tk.Label(root, text="Password").grid(row=1, sticky='W')
tk.Entry(root).grid(row=0, column=1, sticky='E')
tk.Entry(root).grid(row=1, column=1, sticky='E')
tk.Button(root, text="Login").grid(row=2, column=1, sticky='E')

root.mainloop()

Both work, but why does python recognize it one way one time, and not the other?

Answer 1

from tkinter import *

Loads everything from tkinter module, and puts it in the global namespace.

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import tkinter as tk

Loads everything from tkinter module, and put it all in the tk namespace. So Label is now tk.Label , and W is tk.W

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Your third option, which is better when you only need a few objects from the module, would be:

from tkinter import Label, Entry, Button, W, E, Tk

Etc. Again, better when you just need one or two. Not good for your situation. Just included for completeness.

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^{Fortunately you only have one import * or you'd have a much harder time determining which module everything came from!}

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Edit:

tkinter.W = 'w'
tkinter.E = 'e'
tkinter.S = 's'
tkinter.N = 'n'

They're just constants. You could pass the string value and it would work just as well.