overloading on type?

[Steve Purcell]

Burkhard Kloss wrote:
> in python, I catch myself writing things along the lines of
> 
> class date:
>     def __init__ (self, arg):
>         if type(arg) == types.InstanceType:
>             ....
>         elif type(arg) == types.IntType:
>             ...
> 
> which works, but just seems so *wrong*.


There are cases where this sort of type check is the best way to make a
clear API. A solution might be:

  class Date:
     def __init__(self, millis): # construct with int or long
	 self.millis = millis

  def parse_date(str):
      millis = ...
      return Date(millis)

This is quite common in the standard libraries. There are many module-level
functions that 'return an object of type ...', and the mechanism for
constructing such objects directly is deliberately obscured.

Modules form a convenient namespace for factory methods.

-Steve
         
-- 
Steve Purcell, Pythangelist
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