書名： Tkinter GUI Application Development Blueprints（Second Edition）
作者名： Bhaskar Chaudhary
本章字數： 297字
更新時間： 2021-06-24 18:35:03

Ways to create widgets

There are two ways to create widgets in Tkinter.

The first way involves creating a widget in one line and then adding the pack() method (or other geometry managers) in the next line, as follows:

my_label = tk.Label(root, text="I am a label widget")
my_label.pack()

Alternatively, you can write both the lines together, as follows:

tk.Label(root, text="I am a label widget").pack()

You can either save a reference to the widget created ( my_label, as in the first example), or create a widget without keeping any reference to it (as demonstrated in the second example).

You should ideally keep a reference to the widget in case the widget has to be accessed later on in the program. For instance, this is useful in case you need to call one of its internal methods or for its content modification. If the widget state is supposed to remain static after its creation, you need not keep a reference to the widget.

Note that calls to pack() (or other geometry managers) always return None. So, consider a situation where you create a widget, and add a geometry manager (say, pack()) on the same line, as follows: my_label = tk.Label(...).pack(). In this case, you are not creating a reference to the widget. Instead, you are creating a None type object for the my_label variable. So, when you later try to modify the widget through the reference, you get an error because you are actually trying to work on a None type object. If you need a reference to a widget, you must create it on one line and then specify its geometry (like pack()) on the second line, as follows:
my_label = tk.Label(...)
my_label.pack()
This is one of the most common mistakes committed by beginners.

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Tkinter GUI Application Development Blueprints（Second Edition）

Ways to create widgets