Creating __new__ responsible for initializing objects and __init__ responsible for the object.
__new__: When you create an object called, it will return an instance of the current object
__init__: After creating the object invocation, some examples of the current object initialization, no return value
1. In the class, and if __new__ __init__ exist, it will give priority to calls __new__
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class
ClsTest(
object
):
def
__init__(
self
):
print
(
"init"
)
def
__new__(
cls
,
*
args,
*
*
kwargs):
print
(
"new"
)
ClsTest()
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Output:
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1
|
new
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2. If the returned instance of an object __new__, implicitly calling __init__
Code examples:
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class
ClsTest(
object
):
def
__init__(
self
):
print
(
"init"
)
def
__new__(
cls
,
*
args,
*
*
kwargs):
print
(
"new %s"
%
cls
)
return
object
.__new__(
cls
,
*
args,
*
*
kwargs)
ClsTest()
|
Output:
|
1
2
|
new <
class
'__main__.ClsTest'
>
init
|
3. __new__ method returns an object constructed, __ init__ does not. __init__ no return value.
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class
ClsTest(
object
):
def
__init__(
cls
):
cls
.x
=
2
print
(
"init"
)
return
cls
ClsTest()
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Output:
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4
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init
Traceback (most recent call last):
File
"<stdin>"
, line
1
,
in
<module>
TypeError: __init__() should
return
None
,
not
'ClsTest'
|
4. If __new__ not return the correct instance of the current class cls, it is not __init__ is called, even the instance of the parent class is not OK
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class
ClsTest1(
object
):
pass
class
ClsTest2(ClsTest1):
def
__init__(
self
):
print
(
"init"
)
def
__new__(
cls
,
*
args,
*
*
kwargs):
print
(
"new %s"
%
cls
)
return
object
.__new__(ClsTest1,
*
args,
*
*
kwargs)
b
=
ClsTest2()
print
(
type
(b))
|
Output:
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1
2
|
new <
class
'__main__.ClsTest2'
>
<
class
'__main__.ClsTest1'
>
|
