When I was reading open source, there was a method that was return self, and I didn't know what would happen if I did this, so make a note.
class Car1(object):
def __init__(self):
self.miles = 0
self.gas = 0
def drive(self, d):
self.miles += d
self.gas -= d
return self
def fill(self, g):
self.gas += g
return self
class Car2(object):
def __init__(self):
self.miles = 0
self.gas = 0
def drive(self, d):
self.miles += d
self.gas -= d
def fill(self, g):
self.gas += g
if __name__ == '__main__':
car1 = Car1()
car1.fill(100).drive(50)
print 'car1 miles', car1.miles
print 'car1 gas', car1.gas
car2 = Car2()
car2.fill(100).drive(50)
print 'car2 miles', car2.miles
print 'car2 gas', car2.gas
car1 miles 50
car1 gas 50
Traceback (most recent call last):
File "chain.py", line 38, in <module>
car2.fill(100).drive(50)
AttributeError: 'NoneType' object has no attribute 'drive'
Don't do return self in class methods I get an error when trying to do a method chain on an instance of Car2.
If you do return self, you will be able to create a method chain.
With car1, you can connectfill ()anddrive ()as many times as you like.
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