oop - basic inheritance (in python) -

users,

i have basic question concerning inheritance (in python). have 2 classes , 1 of them inherited other like

class   p:     def __init__(self,name):         self.pname  = name  class   c(p):     def __init__(self,name):         self.cname  = name 

is there possibility can create parent object , several child objects refer same parent object? should work that parent object contains several variables , whenever access corresponding variables child access variable form parent. i.e. if change 1 child changed other childes , data stored once in memory (and not copied each child...)

thank in advance.

here possible workaround not consider nice

class p:     def __init__(self, name):         self.pname = name  class c:     def __init__(self, name,pobject):         self.pobject = pobject         self.cname = name 

is state of art or there exist other concepts?

sebastian

thank helping me, name conventions :) still not satisfied. maybe give more advanced example stress want do.

class p:     data = "shareddata"     def __init__(self,newdata):         self.data = newdata       def printname(self):         print self.name   class c(p):     def __init__(self,name):         self.name = name 

now can following

in [33]: c1 = test.c("name1")  in [34]: c2 = test.c("name2")  in [35]: c1.printname() name1  in [36]: c2.printname() name2  in [37]: c1.data out[37]: 'shareddata'  in [38]: c2.data out[38]: 'shareddata' 

and far want. there variable name different every child , parent class accesses individual variables. normal inheritance. there variable data comes parent class , every child access it. however, following not work more

in [39]: c1.data = "tst"  in [40]: c2.data out[40]: 'shareddata'  in [41]: c1.data out[41]: 'tst' 

i want change in c1.data affect c2.data since want variable shared, somehow global variable of parent class.

and more that. want create different instances of p, each having own data variable. , when create new c object want specify p object data should inhetited i.e. shared....

update:

remark comment of @eyquem: this, going direction want. however, __class__.pvar shared among objects of class. want several instances of p may have different pvar. lets assume p1 has pvar=1 , p2 has pvar=2. want create children c1a, c1b, c1c related p1, i.e. if c1a.pvar should acess pvar p1. create c2a, c2b, c2c , if access i.e. c2b.pvar want access pvar p2. since class c inherits pvar class p pvar known c. naive idea if create new instance of c should able specify (existing) p object should used parent object , not create new p object done when calling p.__init__ inside of __init__ of c... sounds simple me, maybe forget something...

update:

so found this discussion pretty question

any suggestions?

update:

the method .class._subclasses_ seems not existing more..

update:

here onother link:

link discussion

there solved copying. not want copy parent class since exists once...

update:

sorry leaving discussion yesterday, bit ill... , thank posts! read through them. thought bit more , here possible solution found

class p(object):     def __init__(self,pvar):         self.pobject    = none         self._pvar  = pvar      @property     def pvar(self):     if self.pobject != none:         return  self.pobject.pvar     else:             return self._pvar     @pvar.setter     def pvar(self,val):     if self.pobject != none:         self.pobject.pvar = val     else:             self._pvar=val      def printname(self):     print self.name   class c(p):     def __init__(self,name,pobject):  #<-- same default `p()`                                            # used instances of `c`,                                            # unless pobject explicitly defined.     p.__init__(self,none)         self.name   = name         self.pobject = pobject   p1  = p("1") p2  = p("2")   c1a = c("c1a",p1) c1b = c("c1b",p1) c1c = c("c1c",p1) c2a = c("c2a",p2) c2b = c("c2b",p2) c2c = c("c2c",p2)   print   id(c1a.pvar) print   id(c1b.pvar) print   id(c1c.pvar) print   id(c2a.pvar) print   id(c2b.pvar) print   id(c2c.pvar) print   id(p1.pvar) print   id(p2.pvar)  print   id(c1a.name) print   id(c1b.name) print   id(c1c.name) print   id(c2a.name) print   id(c2b.name) print   id(c2c.name) 

it bit cumbersome , hope there simpler way achieve this. has feature pvar mentioned in class p , class c not know pvar should according understanding of inheritance. nevertheless when create new instance of c can specify existing instance of p stored in variable pobject. when variable pvar accessed pvar of p-instance stored in variable accessed...

the output given by

3078326816 3078326816 3078326816 3074996544 3074996544 3074996544 3078326816 3074996544 156582944 156583040 156583200 156583232 156583296 156583360 

i read through last comments,

all best, sebastian

update:

i think elegant way following (which not work)

class p(object):     def __init__(self,pvar):         self.pvar   = pvar      def printname(self):         print self.name   class c(p):     def __init__(self,name,pobject):           p = pobject         self.name   = name 

i think python should allow this...

update:

ok, found way achieve this, due explanations eyquem. since hack there should official version same...

def replaceinstance(parent,child):     item in parent.__dict__.items():         child.__dict__.__setitem__(item[0],item[1])         print item  class p(object):     def __init__(self,pvar):         self.pvar   = pvar      def printname(self):     print self.name   class c(p):     def __init__(self,name,pobject):     p.__init__(self,none)     replaceinstance(pobject,self)         self.name   = name    p1  = p("1") p2  = p("2")   c1a = c("c1a",p1) c1b = c("c1b",p1) c1c = c("c1c",p1) c2a = c("c2a",p2) c2b = c("c2b",p2) c2c = c("c2c",p2)   print   id(c1a.pvar) print   id(c1b.pvar) print   id(c1c.pvar) print   id(c2a.pvar) print   id(c2b.pvar) print   id(c2c.pvar) print   id(p1.pvar) print   id(p2.pvar)  print   id(c1a.name) print   id(c1b.name) print   id(c1c.name) print   id(c2a.name) print   id(c2b.name) print   id(c2c.name) 

the output same above

3077745184 3077745184 3077745184 3074414912 3074414912 3074414912 3077745184 3074414912 144028416 144028448 144028480 144028512 144028544 144028576 

update: if id's seem right, last code not work clear test

c1a.pvar    = "newpvar1"  print   c1a.pvar print   c1b.pvar print   c1c.pvar print   c2a.pvar print   c2b.pvar print   c2c.pvar print   p1.pvar print   p2.pvar 

it has output

newpvar1 1 1 2 2 2 1 2 

however version posted first works:

class p(object):     def __init__(self,pvar):         self.pobject    = none         self._pvar  = pvar      @property     def pvar(self):     if self.pobject != none:         return  self.pobject.pvar     else:             return self._pvar     @pvar.setter     def pvar(self,val):     if self.pobject != none:         self.pobject.pvar = val     else:             self._pvar=val      def printname(self):     print self.name   class c(p):     def __init__(self,name,pobject):  #<-- same default `p()`                                            # used instances of `c`,                                            # unless pobject explicitly defined.     p.__init__(self,none)         self.name   = name         self.pobject = pobject   p1  = p("1") p2  = p("2")   c1a = c("c1a",p1) c1b = c("c1b",p1) c1c = c("c1c",p1) c2a = c("c2a",p2) c2b = c("c2b",p2) c2c = c("c2c",p2)   print   id(c1a.pvar) print   id(c1b.pvar) print   id(c1c.pvar) print   id(c2a.pvar) print   id(c2b.pvar) print   id(c2c.pvar) print   id(p1.pvar) print   id(p2.pvar)  print   id(c1a.name) print   id(c1b.name) print   id(c1c.name) print   id(c2a.name) print   id(c2b.name) print   id(c2c.name)     print   "testing\n"  c1a.printname() c1b.printname() c1c.printname() c2a.printname() c2b.printname() c2c.printname()   print   "\n" c1a.name = "c1anewname" c2b.name = "c2bnewname"   c1a.printname() c1b.printname() c1c.printname() c2a.printname() c2b.printname() c2c.printname()   print "pvar\n"  print   c1a.pvar print   c1b.pvar print   c1c.pvar print   c2a.pvar print   c2b.pvar print   c2c.pvar print   p1.pvar print   p2.pvar  print "\n" c1a.pvar    = "newpvar1"  print   c1a.pvar print   c1b.pvar print   c1c.pvar print   c2a.pvar print   c2b.pvar print   c2c.pvar print   p1.pvar print   p2.pvar  print "\n" c2c.pvar    = "newpvar2"  print   c1a.pvar print   c1b.pvar print   c1c.pvar print   c2a.pvar print   c2b.pvar print   c2c.pvar print   p1.pvar print   p2.pvar 

with output

3077745184 3077745184 3077745184 3074414912 3074414912 3074414912 3077745184 3074414912 144028416 144028448 144028480 144028512 144028544 144028576 testing  c1a c1b c1c c2a c2b c2c   c1anewname c1b c1c c2a c2bnewname c2c pvar  1 1 1 2 2 2 1 2   newpvar1 newpvar1 newpvar1 2 2 2 newpvar1 2   newpvar1 newpvar1 newpvar1 newpvar2 newpvar2 newpvar2 newpvar1 newpvar2 

does know why that? not understand internal way python works __dict__ well...

it should work that parent object contains several variables , whenever access corresponding variables child access variable form parent. i.e. if change 1 child changed other childes , data stored once in memory (and not copied each child...)

that's not inheritance.

that's different concept.

your "shared variables" objects can mutated , have references in other objects. nothing interesting.

inheritance different this.