On 12/31/2013 04:03 PM, Zachary Ware wrote:
On Tue, Dec 31, 2013 at 8:35 AM, spir <denis.s...@gmail.com> wrote:
Hello,
I don't remember exactly how to do that. As an example:
class Source (str):
__slots__ = ['i', 'n']
def __init__ (self, string):
self.i = 0 # current matching index in source
self.n = len(string) # number of ucodes (Unicode code points)
#~ str.__init__(self, string)
I thought I needed to call str's __init__, as in the line comented out, but
(1) python refuses with a TypeError (2) all seems to work fine (meaning, the
string is well stored, *implicitely*). Am I missing some point, or is this
the way to do? How does it work? I particular, how does python know which
param to take as source string? (There could be other params to __init__.)
class Source(str):
... __slots__ = ['i', 'n']
... def __init__(self, string):
... self.i = 0
... self.n = len(string)
...
s = Source('testing')
s
'testing'
s.i
0
s.n
7
If you look at the repr of str.__init__, you'll see that it is
inherited from object:
str.__init__
<slot wrapper '__init__' of 'object' objects>
str.__init__ is object.__init__
True
Compare this to the __init__ of list, which is a mutable type:
list.__init__
<slot wrapper '__init__' of 'list' objects>
list.__init__ is not object.__init__
True
Being immutable, str uses __new__ to create a new str object; it
doesn't use __init__ at all. Since you're not overriding __new__ in
your subclass, you don't need to worry about calling str.__new__
because it's already done by the time Source.__init__ is called.
Thank you, Oscar & Zachary. I guess thus the way it is done is correct (for my
case), is it? Seems your last remark shows the source of my confusion: probably,
in past times, I subtyped builtin types and overrided their __new__, thus had to
call the original one.
Would I have to do this if Source had other __init__ params? Or would it work
anyway provided the string remains 1st param? Or what else?
Denis
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