How to achieve inheritance using classmethod factory functions
How do I use/reuse implementations in the parent class when using the classmethod approach for implementing factory functions?
In the example below, class A is fine, but class B is broken.
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = A.from_jdata(B, data)
res.__dict__['extra']='set'
return res
The context is that I'm trying to instantiate instances based on JSON configuration data. The inheritance hierarchy is deeper than just two classes, i.e. there are a number of children of class B. The root of the inheritance hierarchy does some useful stuff in the factory function. Children classes should re-use that but add on some additional operations.
python inheritance factory-pattern
asked Nov 15 at 22:49
Dave
3,66342249
add a comment |
How do I use/reuse implementations in the parent class when using the classmethod approach for implementing factory functions?
In the example below, class A is fine, but class B is broken.
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = A.from_jdata(B, data)
res.__dict__['extra']='set'
return res
The context is that I'm trying to instantiate instances based on JSON configuration data. The inheritance hierarchy is deeper than just two classes, i.e. there are a number of children of class B. The root of the inheritance hierarchy does some useful stuff in the factory function. Children classes should re-use that but add on some additional operations.
python inheritance factory-pattern
asked Nov 15 at 22:49
Dave
3,66342249
I've done this in the past through registration of children and making the parent discriminate between children for deserialization.
– erip
Nov 15 at 22:51
add a comment |
How do I use/reuse implementations in the parent class when using the classmethod approach for implementing factory functions?
In the example below, class A is fine, but class B is broken.
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = A.from_jdata(B, data)
res.__dict__['extra']='set'
return res
The context is that I'm trying to instantiate instances based on JSON configuration data. The inheritance hierarchy is deeper than just two classes, i.e. there are a number of children of class B. The root of the inheritance hierarchy does some useful stuff in the factory function. Children classes should re-use that but add on some additional operations.
python inheritance factory-pattern
asked Nov 15 at 22:49
Dave
3,66342249
How do I use/reuse implementations in the parent class when using the classmethod approach for implementing factory functions?
In the example below, class A is fine, but class B is broken.
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = A.from_jdata(B, data)
res.__dict__['extra']='set'
return res
The context is that I'm trying to instantiate instances based on JSON configuration data. The inheritance hierarchy is deeper than just two classes, i.e. there are a number of children of class B. The root of the inheritance hierarchy does some useful stuff in the factory function. Children classes should re-use that but add on some additional operations.
python inheritance factory-pattern
python inheritance factory-pattern
asked Nov 15 at 22:49
Dave
3,66342249
asked Nov 15 at 22:49
Dave
3,66342249
asked Nov 15 at 22:49
Dave
3,66342249
asked Nov 15 at 22:49
Dave
3,66342249
asked Nov 15 at 22:49
Dave
3,66342249
3,66342249
I've done this in the past through registration of children and making the parent discriminate between children for deserialization.
– erip
Nov 15 at 22:51
add a comment |
I've done this in the past through registration of children and making the parent discriminate between children for deserialization.
– erip
Nov 15 at 22:51
I've done this in the past through registration of children and making the parent discriminate between children for deserialization.
– erip
Nov 15 at 22:51
I've done this in the past through registration of children and making the parent discriminate between children for deserialization.
– erip
Nov 15 at 22:51
add a comment |
1 Answer
1
active
oldest
votes
Use super, of course:
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = super().from_jdata(data)
# res = super(B, cls).from_jdata(data) # in python 2
res.__dict__['extra']='set'
return res
In action:
In [6]: b = B.from_jdata({'_id':42, 'foo':'bar'})
In [7]: vars(b)
Out[7]: {'foo': 'bar', 'uuid': 42, 'extra': 'set'}
Note, what you were trying to do won't work because @classmethod creates a descriptor that binds the class when called from either the class or the instance. You would have to access the raw function using something like:
res = A.__dict__['from_jdata'].__func__(B, data)
To make it work, but just use super, that's what it is for.
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
1
@Dave I edited in to a comment:# res = super(B, cls).from_jdata(data) # in python 2
– juanpa.arrivillaga
Nov 15 at 23:13
it looks likesuper(B, cls).from_jdata(data)works
– Dave
Nov 15 at 23:13
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Use super, of course:
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = super().from_jdata(data)
# res = super(B, cls).from_jdata(data) # in python 2
res.__dict__['extra']='set'
return res
In action:
In [6]: b = B.from_jdata({'_id':42, 'foo':'bar'})
In [7]: vars(b)
Out[7]: {'foo': 'bar', 'uuid': 42, 'extra': 'set'}
Note, what you were trying to do won't work because @classmethod creates a descriptor that binds the class when called from either the class or the instance. You would have to access the raw function using something like:
res = A.__dict__['from_jdata'].__func__(B, data)
To make it work, but just use super, that's what it is for.
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
1
@Dave I edited in to a comment:# res = super(B, cls).from_jdata(data) # in python 2
– juanpa.arrivillaga
Nov 15 at 23:13
it looks likesuper(B, cls).from_jdata(data)works
– Dave
Nov 15 at 23:13
add a comment |
Use super, of course:
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = super().from_jdata(data)
# res = super(B, cls).from_jdata(data) # in python 2
res.__dict__['extra']='set'
return res
In action:
In [6]: b = B.from_jdata({'_id':42, 'foo':'bar'})
In [7]: vars(b)
Out[7]: {'foo': 'bar', 'uuid': 42, 'extra': 'set'}
Note, what you were trying to do won't work because @classmethod creates a descriptor that binds the class when called from either the class or the instance. You would have to access the raw function using something like:
res = A.__dict__['from_jdata'].__func__(B, data)
To make it work, but just use super, that's what it is for.
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
1
@Dave I edited in to a comment:# res = super(B, cls).from_jdata(data) # in python 2
– juanpa.arrivillaga
Nov 15 at 23:13
it looks likesuper(B, cls).from_jdata(data)works
– Dave
Nov 15 at 23:13
add a comment |
Use super, of course:
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = super().from_jdata(data)
# res = super(B, cls).from_jdata(data) # in python 2
res.__dict__['extra']='set'
return res
In action:
In [6]: b = B.from_jdata({'_id':42, 'foo':'bar'})
In [7]: vars(b)
Out[7]: {'foo': 'bar', 'uuid': 42, 'extra': 'set'}
Note, what you were trying to do won't work because @classmethod creates a descriptor that binds the class when called from either the class or the instance. You would have to access the raw function using something like:
res = A.__dict__['from_jdata'].__func__(B, data)
To make it work, but just use super, that's what it is for.
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
Use super, of course:
class A(object):
def __init__(self, **kwds):
self.__dict__.update(kwds)
@classmethod
def from_jdata(cls, data):
if '_id' in data:
data['uuid'] = data['_id']
del data['_id']
return cls(**data)
class B(A):
def __init__(self, **kwds):
super(B, self).__init__(**kwds)
@classmethod
def from_jdata(cls, data):
# goal: make an instance of B,
# using the logic that is implemented in A.from_jdata
# But does some extra stuff, akin to:
res = super().from_jdata(data)
# res = super(B, cls).from_jdata(data) # in python 2
res.__dict__['extra']='set'
return res
In action:
In [6]: b = B.from_jdata({'_id':42, 'foo':'bar'})
In [7]: vars(b)
Out[7]: {'foo': 'bar', 'uuid': 42, 'extra': 'set'}
Note, what you were trying to do won't work because @classmethod creates a descriptor that binds the class when called from either the class or the instance. You would have to access the raw function using something like:
res = A.__dict__['from_jdata'].__func__(B, data)
To make it work, but just use super, that's what it is for.
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
edited Nov 15 at 23:19
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
answered Nov 15 at 23:03
juanpa.arrivillaga
37k33470
37k33470
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
1
@Dave I edited in to a comment:# res = super(B, cls).from_jdata(data) # in python 2
– juanpa.arrivillaga
Nov 15 at 23:13
it looks likesuper(B, cls).from_jdata(data)works
– Dave
Nov 15 at 23:13
add a comment |
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
1
@Dave I edited in to a comment:# res = super(B, cls).from_jdata(data) # in python 2
– juanpa.arrivillaga
Nov 15 at 23:13
it looks likesuper(B, cls).from_jdata(data)works
– Dave
Nov 15 at 23:13
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
How to in python2.7 where arguments are required?
– Dave
Nov 15 at 23:10
1
1
@Dave I edited in to a comment:
# res = super(B, cls).from_jdata(data) # in python 2– juanpa.arrivillaga
Nov 15 at 23:13
@Dave I edited in to a comment:
# res = super(B, cls).from_jdata(data) # in python 2– juanpa.arrivillaga
Nov 15 at 23:13
it looks like
super(B, cls).from_jdata(data) works– Dave
Nov 15 at 23:13
it looks like
super(B, cls).from_jdata(data) works– Dave
Nov 15 at 23:13
add a comment |
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I've done this in the past through registration of children and making the parent discriminate between children for deserialization.
– erip
Nov 15 at 22:51