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Design Pattern for accessing subclass attributes - UGuntupalli - Jul-30-2019
All,
I am looking for guidance on what would be good design pattern to use / implement given a particular problem.
Problem Statement:
Let us say we would like to define a class that defines i-phone. Please note the below example is only for illustration.
If a user of this class wants to determine the mfg.year which is only set in the sub-class, what is the best way to get that information, without knowing which sub-class to call.
The user is always only going to instantiate the base class that is of the IPhone().
class IPhone():
def __init__(self,ver):
self.ver = ver
self.phone_factory()
def phone_factory(self):
if self.ver == '3G':
return IPhone3G()
elif self.ver == '3GS':
return IPhone3GS()
elif self.ver == '4':
return IPhone4()
elif self.ver == '4s':
return IPhone4s()
elif self.ver == '5':
return IPhone5()
else:
pass
class IPhone3G():
def __init__(self):
self.year = 2007
class IPhone3GS():
def __init__(self):
self.year = 2009
class IPhone4():
def __init__(self):
self.year = 2010
class IPhone4s():
def __init__(self):
self.year = 2011
class IPhone5():
def __init__(self):
self.year = 2012Potential Solution: One way I can think of addressing this problem is by doing the following:
class IPhone():
def __init__(self,ver):
self.ver = ver
self.phone_factory()
def phone_factory(self):
if self.ver == '3G':
t = IPhone3G()
self.year = t.year
elif self.ver == '3GS':
t = IPhone3GS()
self.year = t.year
elif self.ver == '4':
t = IPhone4()
self.year = t.year
elif self.ver == '4s':
t = IPhone4s()
self.year = t.year
elif self.ver == '5':
t = IPhone5()
self.year = t.year
else:
pass
class IPhone3G():
def __init__(self):
self.year = 2007
class IPhone3GS():
def __init__(self):
self.year = 2009
class IPhone4():
def __init__(self):
self.year = 2010
class IPhone4s():
def __init__(self):
self.year = 2011
class IPhone5():
def __init__(self):
self.year = 2012But, is this a good approach ? I have looked at class methods and static methods as alternative options but I am not really sure what is the best approach. Can anybody advice?
RE: Design Pattern for accessing subclass attributes - woooee - Jul-30-2019
Quote:If a user of this class wants to determine the mfg.yearBetter to store the data in a dictionary IMHO. Have the key point to a list if you want to store more than the year.
class IPhone():
def __init__(self,ver):
self.ver = ver
self.ver_dic={'3G': 2007,
'3GS':2009,
'4': 2010,
'4s': 2011,
'5': 2012}
self.phone_factory()
def phone_factory(self):
if self.ver in self.ver_dic:
return self.ver_dic[self.ver]
else:
## Python returns None if there is no return
## so this is not necessary
return None
RE: Design Pattern for accessing subclass attributes - UGuntupalli - Jul-30-2019
I should elaborate a little further. Apologies.
mfg.year is just one attribute that I tried to demonstrate my problem with. Imagine if there were many such pieces of information,
for e.g:
1. Which apple factory location was that phone made in ?
2. Which apple warehouse did it get shipped to ?
3. How was it sold ? (online vs in store)
All these pieces of information would typically be stored in different databases, so separating them into sub-classes provides the flexibility to pull data from the correct database(s). However, what I am not sure of is since the user does not know which type of iphone he/she is instantiating, how to provide the user with visibility to sub-class attributes.