Why is `None` returned instead of tkinter.Entry object? [duplicate]

This question already has answers here: Tkinter: AttributeError: NoneType object has no attribute <attribute name> (4 answers) Closed 10 months ago.

I'm new to python, poking around and I noticed this:

from tkinter import *
def test1():
    root = Tk()
    txtTest1 = Entry(root).place(x=10, y=10)
    print(locals())
def test2():
    root = Tk()
    txtTest2 = Entry(root)
    txtTest2.place(x=10, y=10)#difference is this line
    print(locals())
test1()
test2()

开发者_运维百科

outputs contain:

'txtTest1': None

'txtTest2': <tkinter.Entry object at 0x00EADD70>

Why does test1 have a None instead of <tkinter.Entry object at ...?

I'm using python 3.2 and PyScripter.

---

The place method of Entry doesn't return a value. It acts in-place on an existing Entry variable.

---

because Entry.place() returns None

in a more C-like language you could do:

(txtTest1 = Entry(root)).place(x=10, y=10)

and txtText1 would be the Entry object, but that syntax is illegal in Python.

---

You are creating an object (txtTest1) and then calling a method on that object (place). Because you code that as one expression, the result of the final method is what gets returned. place returns None, so txtTest1 gets set to None

If you want to save a reference to a widget you need to separate the creation from the layout (which is a Good Thing To Do anyway...)

txtTest1 = Entry(root)
txtTest1.place(x=10, y=10)