Re: Inheriting dictionary
On Tuesday 18 August 2009 21:44:55 Pavel Panchekha wrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
Its not inheritance, but have you looked at the update method?
-Hendrik
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Inheriting dictionary
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Inheriting dictionary
18-08-2009 o 21:44:55 Pavel Panchekha pavpanche...@gmail.com wrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
AFAIN -- no. But you can easily implement it in Python with rather
small loss of speed...
class InheritDict(dict):
class NoParent(object):
def __getitem__(self, key):
raise KeyError('There is no %r key in the hierarchy' % key)
def __nonzero__(self):
return False
noparent = NoParent()
def __init__(self, *args, **kwargs):
parent = kwargs.pop('inherit_from', self.noparent)
dict.__init__(self, *args, **kwargs)
self.parent = parent
def __getitem__(self, key):
try:
return dict.__getitem__(self, key)
except KeyError:
return self.parent[key]
Did you do it in similar way? (just curiosity) :-)
Regards,
*j
--
Jan Kaliszewski (zuo) z...@chopin.edu.pl
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Re: Inheriting dictionary
On Tue, Aug 18, 2009 at 2:44 PM, Pavel Panchekha pavpanche...@gmail.comwrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
Why complicate this with a custom object? Just use regular dicts and make b
a copy of a.
a = {1: 'one', 2: 'two', 4: 'four'}
b = dict(a)
b[3] = 'three'
b[4] = 'foobar'
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Re: Inheriting dictionary
On Aug 18, 4:23 pm, Jan Kaliszewski z...@chopin.edu.pl wrote:
18-08-2009 o 21:44:55 Pavel Panchekha pavpanche...@gmail.com wrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
AFAIN -- no. But you can easily implement it in Python with rather
small loss of speed...
class InheritDict(dict):
class NoParent(object):
def __getitem__(self, key):
raise KeyError('There is no %r key in the hierarchy' % key)
def __nonzero__(self):
return False
noparent = NoParent()
def __init__(self, *args, **kwargs):
parent = kwargs.pop('inherit_from', self.noparent)
dict.__init__(self, *args, **kwargs)
self.parent = parent
def __getitem__(self, key):
try:
return dict.__getitem__(self, key)
except KeyError:
return self.parent[key]
Did you do it in similar way? (just curiosity) :-)
Regards,
*j
--
Jan Kaliszewski (zuo) z...@chopin.edu.pl
I implemented it in a similar way (instead of a try block, an if
block, which works a tiny bit faster; also have a multiple-parents
case, but its rare, and I could do that in Python without much loss of
speed). Pity that there's no C version; this InheritDict is kind of
the core of my application (in a very basic test, I have 329901 calls
to __getitem__).
Oh well; I'll see if I can optimize the __getattr__ function with
minor tweaking. Thanks for your help.
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Re: Inheriting dictionary
18-08-2009 o 22:27:41 Nat Williams nat.willi...@gmail.com wrote:
On Tue, Aug 18, 2009 at 2:44 PM, Pavel Panchekha
pavpanche...@gmail.comwrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
Why complicate this with a custom object? Just use regular dicts and
make b a copy of a.
a = {1: 'one', 2: 'two', 4: 'four'}
b = dict(a)
b[3] = 'three'
b[4] = 'foobar'
Because, as I understand Pavel's intent, it has to work dynamically
(e.g. changes in 'a' reflect in behaviour of 'b'), and obviously not
only for such trivial examples like above.
*j
--
Jan Kaliszewski (zuo) z...@chopin.edu.pl
--
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Re: Inheriting dictionary
On Aug 18, 5:11 pm, Jan Kaliszewski z...@chopin.edu.pl wrote:
18-08-2009 o 22:27:41 Nat Williams nat.willi...@gmail.com wrote:
On Tue, Aug 18, 2009 at 2:44 PM, Pavel Panchekha
pavpanche...@gmail.comwrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
Why complicate this with a custom object? Just use regular dicts and
make b a copy of a.
a = {1: 'one', 2: 'two', 4: 'four'}
b = dict(a)
b[3] = 'three'
b[4] = 'foobar'
Because, as I understand Pavel's intent, it has to work dynamically
(e.g. changes in 'a' reflect in behaviour of 'b'), and obviously not
only for such trivial examples like above.
*j
--
Jan Kaliszewski (zuo) z...@chopin.edu.pl
That is indeed the point.
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Re: Inheriting dictionary
On Tue, Aug 18, 2009 at 6:08 PM, Simon Formansajmik...@gmail.com wrote:
On Aug 18, 3:44 pm, Pavel Panchekha pavpanche...@gmail.com wrote:
I want a dictionary that will transparently inherit from a parent
dictionary. So, for example:
a = InheritDict({1: one, 2: two, 4: four})
b = InheritDict({3: three, 4: foobar}, inherit_from=a)
a[1] # one
a[4] # four
b[1] # one
b[3] # three
b[4] # foobar
I've written something like this in Python already, but I'm wondering
if something like this already exists, preferably written in C, for
speed.
I would consider something like the following:
a = {1: one, 2: two, 4: four}
b = {3: three, 4: foobar}
from functools import partial
def getter(first, second, key):
try:
return first(key)
except KeyError:
return second(key)
f = partial(getter, b.__getitem__, a.__getitem__)
# Or, if you know you'll be getting a lot of KeyErrors, you
# can use get() instead of __getitem__().
def getter1(first, second, key, sentinel=None):
item = first(key, sentinel)
if item is sentinel:
item = second(key)
return item
g = partial(getter1, b.get, a.__getitem__)
HTH,
~Simon
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Since you're going for speed the overhead of using partial (which
creates a wrapper object around the getter function) can be replaced
by something like this:
def makeGetter(first, second):
def getter(key):
try:
return first(key)
except KeyError:
return second(key)
return getter
f = makeGetter(b.__getitem__, a.__getitem__)
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Inheriting dictionary attributes and manipulate them in subclasses
Hi,
I just stumbled upon the following behaviour.
class base():
... dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '2', '2': '2'}
This is not what I have excepted.
Although I know the solution to get what I want...
class base():
... def __init__(self):
... self.dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... base.__init__(self)
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '1', '2': '2'}
... I wonder if there is a special reason for the behaviour in the
first example.
Shouldn't the first example behave like the second?
cheers
Dominik
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Re: Inheriting dictionary attributes and manipulate them in subclasses
Dominik Ruf wrote:
Hi,
I just stumbled upon the following behaviour.
class base():
... dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '2', '2': '2'}
This is not what I have excepted.
Although I know the solution to get what I want...
class base():
... def __init__(self):
... self.dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... base.__init__(self)
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '1', '2': '2'}
... I wonder if there is a special reason for the behaviour in the
first example.
Shouldn't the first example behave like the second?
No, because you are creating *classvariables* when declaring things like
this:
class Foo(object):
bar = {}
If these are mutable, changing them will change them for *all* instances.
OTOH, when assigning to an instance, this will create an
*instance*-variable. Which is what
self.some_name = some_value
does.
Diez
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Variables vs attributes [was Re: Inheriting dictionary attributes and manipulate them in subclasses]
On Fri, 17 Apr 2009 17:48:55 +0200, Diez B. Roggisch wrote: No, because you are creating *classvariables* when declaring things like this: ... OTOH, when assigning to an instance, this will create an *instance*-variable. Which is what If an integer variable is an integer, and a string variable is a string, and float variable is a float, and a list variable is a list (there's a pattern here), shouldn't a class variable be a class and an instance variable be an instance? I had never noticed the usage of variable to mean attribute until a few months ago. What's going on? Why did people decide that confusing variables and attributes of variables was a good thing? What's next, describing dictionary keys as dictionary variables? Sorry to pick on Diez, he's not the only one, just the latest example. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
