Multiple constructor with Python
I have a class A that can be generated from two different ways.
- a = A(path_to_xml_file)
- a = A(listA, listB)
The first method has file path as an input to parse from XML file to get listA, and listB. The second method is given two lists.
I can think of two ways to implement multiple constructor. What do you th开发者_高级运维ink? What method normally Python guys use for this case?
Check the type
class A():
def __init__(self, arg1, arg2 = None):
if isinstance(arg1, str):
...
elif isinstance(arg1, list):
...
a = A("abc")
b = A([1,2,3],[4,5,6])
Make different builders
class A2():
def __init__(self):
pass
def genFromPath(self, path):
...
def genFromList(self, list1, list2):
...
a = A2()
a.genFromPath("abc")
b = A2()
b.genFromList([1,2,3],[4,5,6])
Make the constructor take the two lists. Write a factory classmethod that parses the XML and returns the object.
Use classmethod
for second one
class A(object):
@classmethod
def from_string(cls, string):
# ...
@classmethod
def from_lists(cls, list1, list2):
# ...
Use module's functions
def from_string(string):
# ...
def from_lists(list1, list2):
# ...
class A(object):
pass
Since the number of arguments passed to the initializer is different in each case, you can avoid type-checking by using the extended call syntax:
class A(object):
def __init__(self, *args):
if len(args) == 1:
path = args[0]
...
elif len(args) == 2:
list1 = args[0]
list2 = args[1]
...
else:
raise SomeException()
Looking at the problem more closely, I'd suggest having the class take two lists, and include a helper function in the module:
class A(object):
def __init__(self, list1, list2):
# Init from lists here
pass
def create_A_from_path(path):
list1, list2 = parse_xml_into_lists(path)
return A(list1, list2)
class A(object):
@staticmethod
def from_string(str):
obj =A()
obj.str = str
return obj
@staticmethod
def from_list(lis):
obj = A()
obj.lis = lis
return obj
>>>
(obj1, obj2) = A.from_string('hello'), A.from_list(['one', 'two'])
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