[Tutor] Declaring methods in modules.
steve at pearwood.info
Sun Apr 11 18:37:15 CEST 2010
On Sun, 11 Apr 2010 10:30:54 pm Ray Parrish wrote:
> I am working on some stuff, and I would like to be able to write a
> module which can be imported, and after it's been imported I would
> like to be able to access it's functions as methods.
> In other words, if I do the import of module ISPdetector, I want to
> then be able to make calls like the following -
> ipAddress = "188.8.131.52"
> emails = ipAddress.GetEmailAddresses()
Can't be done -- in Python, built-in types like strings can't have new
methods added to them, and thank goodness for that! The ability to
monkey-patch builtins is more dangerous than useful.
But you can subclass builtins, as Alan suggested:
# module ISPdetector
# another module
ipAddress = ISPdetector.MyString("184.108.40.206")
emails = ipAddress.GetEmailAddresses()
But that is a strange API design. IP addresses aren't strings, they're
integers, and although they are commonly written in quad-dotted form as
a string, you don't want to treat them as strings. For example,
something like ipAddress.replace('2', 'P') makes no sense.
Also, making GetEmailAddresses a method of an IP address implies that
address *have* email addresses, which is nonsense. People have email
addresses. Computer accounts have email addresses. Particular email
*messages* come from an IP address, but IP addresses don't have email
addresses. A better name would be ipaddress.find_email_from().
So I would suggest the best API is either to create an IP address class
(or better still, don't re-invent the wheel, use one of the fine
existing IP address modules already written), or write functions in the
module and just call them:
ipAddress = "220.127.116.11"
emails = find_email_from(ipAddress)
Remember, in Python methods are just syntactic sugar for function calls.
obj.method(arg) is just another way of spelling method(obj, arg).
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