How do I learn operator overriding?

[Erik Max Francis]

python at sarcastic-horse.com wrote:

> The only problem is that I have no idea how to override operators in
> python.  Can anyone give me a few trivial examples of how it is done?

Just override the __sub__ method:

>>> class Date:
...  def __init__(self, year, quarter):
...   self.year = year
...   self.quarter = quarter
...  def quarters(self):
...   return self.year*4 + self.quarter
...  def __sub__(self, other):
...   return self.quarters() - other.quarters()
... 
>>> Date
<class __main__.Date at 0x402e053c>
>>> q1 = Date(2001, 1)
>>> q4 = Date(2001, 4)
>>> q4 - q1
3

> And, on a completely unrelated note, I am getting a truly amazing
> amount
> of spam today.  Anyone else?

Yep.  I've gotten 262 MB since 2 am this morning.  Another worm is out
and about, I'd presume.

-- 
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