asks the packer to expand the allocated space for the widget in general into any unclaimed space in the widget' parent fill option can be used to stretch the widget to occupy all of its allocated space combinations of these two options produce different layout and resizing effectssome of which become meaningful only when there are multiple widgets in window for exampleusing expand without fill centers the widget in the expanded spaceand the fill option can specify vertical stretching only (fill= )horizontal stretching only (fill= )or both (fill=bothby providing these constraints and attachment sides for all widgets in guialong with packing orderwe can control the layout in fairly precise terms in later we'll find that the grid geometry manager uses different resizing protocol entirelybut it provides similar control when needed all of this can be confusing the first time you hear itand we'll return to this later but if you're not sure what an expand and fill combination will dosimply try it out--this is pythonafter all for nowremember that the combination of expand=yes and fill=both is perhaps the most common settingit means "expand my space allocation to occupy all available space on my sideand stretch me to fill the expanded space in both directions for our "hello worldexamplethe net result is that the label grows as the window is expandedand so is always centered configuring widget options and window titles so farwe've been telling tkinter what to display on our label by passing its text as keyword argument in label constructor calls it turns out that there are two other ways to specify widget configuration options in example - the text option of the label is set after it is constructedby assigning to the widget' text key widget objects overload (interceptindex operations such that options are also available as mapping keysmuch like dictionary example - pp \gui\intro\gui py--option keys from tkinter import widget label(widget['text''hello gui world!widget pack(side=topmainloop(more commonlywidget options can be set after construction by calling the widget config methodas in example - tkinter coding alternatives