Printing of Objects
- When an object is printed using
print(object), Python calls its__str__()method to get a readable string.
Example (from 17.6):
class Time:
def __str__(self):
return '%.2d:%.2d:%.2d' % (self.hour, self.minute, self.second)
time = Time(9, 45)
print(time) # Output: 09:45:00
This provides a human-readable output when printing an object.
Objects Are Mutable
- In Python, objects like instances of classes are mutable.
- This means their attributes can be changed after the object is created.
Example (from 15.5):
box = Rectangle() box.width = 100.0 box.height = 200.0 box.width = box.width + 50 box.height = box.height + 100
Modified values:
box.width → 150.0 box.height → 300.0
Functions can also modify objects:
def grow_rectangle(rect, dwidth, dheight):
rect.width += dwidth
rect.height += dheight
Calling:
grow_rectangle(box, 50, 100) # Now box.width = 200.0, box.height = 400.0
This shows that when an object is passed to a function, changes to its attributes affect the original object.