Explain __init__() and __str__() methods with examples. Discuss type-based dispatch in Python
Answer:-
__init__() Method
__init__is a special method used to initialize object attributes.- It is called automatically when a new object is created.
Example (from 17.5):
class Time:
def __init__(self, hour=0, minute=0, second=0):
self.hour = hour
self.minute = minute
self.second = second
Usage:
time = Time(9, 45)
This sets time.hour = 9, time.minute = 45, and time.second = 0.
__str__() Method
__str__is used to define the string representation of an object.- It is called automatically by the
print()function.
Example (from 17.6):
class Time:
def __str__(self):
return '%.2d:%.2d:%.2d' % (self.hour, self.minute, self.second)
Usage:
time = Time(9, 45) print(time) # Output: 09:45:00
Type-Based Dispatch
- A method uses
isinstance()to behave differently based on the type of argument passed. - Useful in operator overloading or when an operation depends on operand type.
Example (from 17.8):
def __add__(self, other):
if isinstance(other, Time):
return self.add_time(other)
else:
return self.increment(other)
Usage:
start = Time(9, 45) duration = Time(1, 35) print(start + duration) # Time + Time print(start + 1337) # Time + int
This allows the same + operator to work with both Time and int types by dispatching based on the argument type.