Objects are mutable
We can change the state of an object by making an assignment to one of its attributes. For example, to change the size of a rectangle without changing its position, you can modify the values of width and height:
box.width = box.width + 50
box.height = box.height + 100
You can also write functions that modify objects. For example, grow_rectangle takes a Rectangle object and two numbers, dwidth and dheight, and adds the numbers to the width and height of the rectangle:
def grow_rectangle(rect,dwidth,dheight):
rect.width += dwidth
rect.height += dheight
Here is an example that demonstrates the effect:
Inside the function, rect is an alias for box, so if the function modifies rect, box changes.
from Thinking in Python
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