structs in python

[Fernando Pérez]

Christophe Delord wrote:

> 
> The dict can be the __dict__ attribute of a particular class :
> 
> 
> class Record:
> 
> def __init__(self, **kw):
> self.__dict__.update(kw);
> 
> p = Record(x=10, y=11, color='blue')
> 
> print p.x

such a class can then be conveniently updated later with the following:

def with(object, **args):
    """Set multiple attributes for an object, similar to Pascal's with.

    Example:
    with(jim,
         born = 1960,
         haircolour = 'Brown',
         eyecolour = 'Green')

    Credit: Greg Ewing, in
    http://mail.python.org/pipermail/python-list/2001-May/040703.html"""

    object.__dict__.update(args)


If you want a full-blown class which implements struct-like functionality 
with both dictionary-type (s['blah']) and struct-type (s.blah) access for its 
data members, you can use my Struct.py from:
 http://windom.colorado.edu/~fperez/python/misc/Struct.py
An html syntax-highligted version is at:
 http://windom.colorado.edu/~fperez/python/misc/Struct.py.html

Having both kinds of access allows explicit named acess:
s['blah'] == s.blah
but also access by variable:
x='blah'
s[x] == s['blah']

Obviously, any '.' access is explicit by name always.

Besides allowing both types of access (dict and struct), it has all the 
behavior of a dict (keys, values, items, update, get, setdefault, etc) plus a 
fancy 'merge' method which is a flexible version of update. It allows you to 
update a Struct with fine control over what to do when collisions are found 
(update simply overwrites old data, not always what you want). This makes it 
very useful for keeping configuration information which needs to be updated 
in various forms, for example.

I've successfully used this class in several projects, and it's extremely 
convenient. Note however that it was coded for convenience, not speed. If you 
use it and find any bugs in it, please let me know.


Note that it requires the following function from a module I have around 
called genutils. You can simply paste the following in Struct.py and remove 
the import line:

def list2dict2(lst,default=''):
    """Takes a list and turns it into a dict.
    Much slower than list2dict, but more versatile. This version can take
    lists with sublists of arbitrary length (including sclars)."""

    dic = {}
    for elem in lst:
        if type(elem) in (types.ListType,types.TupleType):
            size = len(elem)
            if  size == 0:
                pass
            elif size == 1:
                dic[elem] = default
            else:
                k,v = elem[0], elem[1:]
                if len(v) == 1: v = v[0]
                dic[k] = v
        else:
            dic[elem] = default
    return dic