Can one get "for x in y" to work for non builtin classes?

[Preben Randhol]

Hi

I'm making a kind of ordered dictionary class. It is not exactly a
dictionary, but it uses a list and dictionary to store the data.

Something like:

class dbase(list):
'''Database class keeping track of the order and data'''

def __init__(self):
self.__data = {}
self.__order = []
self.__uniq_id = 0

I'm just wondering if it is possible to get my class to work so that if
one do:


d=dbase()
d.append("Data")
d.append([1,2])

one can do like this to iterate over the data.

for x in d:
...

I'm looking at the list class but I don't quite understand from pydoc
which __ __ methods I have to implement to get the above to work.

Thanks in advance

Preben

 

[Preben Randhol]

class dbase(list):

Sorry the definition of the class is:

class dbase(object):

it doesn't derive from the list class.

Preben

 

[Giles Brown]

Sorry the definition of the class is:

class dbase(object):

it doesn't derive from the list class.

Preben

http://docs.python.org/lib/typeiter.html

 

[castironpi]

http://docs.python.org/lib/typeiter.html

Be careful on your descision to return an ordered iterator or not--
that is, whether it iterates over the dictionary or the list (if I
understand you correctly). If the order's unimportant then please
disregard.

You can also use:

a= [2,3,4]
b= iter( a )
next( b ) 2
next( b ) 3
next( b )

4

 

[Preben Randhol]

On Sun, 2 Mar 2008 08:09:24 -0800 (PST)

Be careful on your descision to return an ordered iterator or not--
that is, whether it iterates over the dictionary or the list (if I
understand you correctly). If the order's unimportant then please
disregard.

I was thinking to iterate over the list which contains the uniq_ids as
order is important

Thanks!

Preben

 

[Preben Randhol]

http://docs.python.org/lib/typeiter.html

Thanks!

 

[M.-A. Lemburg]

Hi

I'm making a kind of ordered dictionary class. It is not exactly a
dictionary, but it uses a list and dictionary to store the data.

Something like:

class dbase(list):
'''Database class keeping track of the order and data'''

def __init__(self):
self.__data = {}
self.__order = []
self.__uniq_id = 0

I'm just wondering if it is possible to get my class to work so that if
one do:


d=dbase()
d.append("Data")
d.append([1,2])

one can do like this to iterate over the data.

for x in d:
...

I'm looking at the list class but I don't quite understand from pydoc
which __ __ methods I have to implement to get the above to work.

The easiest is to implement an iterator which then get's
returned by the .__iter__() method.

http://www.python.org/doc/lib/typeiter.html

It's also possible to implement .__getitem__() and .__len__()
methods and have Python create an iterator on-the-fly. That's
how Python used to work before iterators were added to the
language.

--
Marc-Andre Lemburg
eGenix.com

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[Marc 'BlackJack' Rintsch]

It's also possible to implement .__getitem__() and .__len__()
methods and have Python create an iterator on-the-fly. That's
how Python used to work before iterators were added to the
language.

A suitable `__getitem__()` is enough. The end will be signaled by an
`IndexError`.

Ciao,
Marc 'BlackJack' Rintsch