Why it only realize the last instance when using python singleton pattern
the code is in belows:
class A(object):
__instance = None
def __new__(cls, *args, **kwargs):
if cls.__instance is None:
cls.__instance = object.__new__(cls)
return cls.__instance
else:
return cls.__instance
def __init__(self, book):
self.book = book
def pr(self):
print(self.book)
if __name__ == "__main__":
b = A("wind")
a = A("good")
print(a is b)
print(a.pr())
print(b.pr())
the result is
True
good
None
good
None
why the result is not:
True
wind
good
where is wrong with the code?
python singleton
add a comment |
the code is in belows:
class A(object):
__instance = None
def __new__(cls, *args, **kwargs):
if cls.__instance is None:
cls.__instance = object.__new__(cls)
return cls.__instance
else:
return cls.__instance
def __init__(self, book):
self.book = book
def pr(self):
print(self.book)
if __name__ == "__main__":
b = A("wind")
a = A("good")
print(a is b)
print(a.pr())
print(b.pr())
the result is
True
good
None
good
None
why the result is not:
True
wind
good
where is wrong with the code?
python singleton
Ita
isb
how shouldpr()
return different values?
– Klaus D.
Nov 23 at 2:51
The wind is the first instance. Why it notTrue wind wind
,
– littlely
Nov 23 at 2:56
add a comment |
the code is in belows:
class A(object):
__instance = None
def __new__(cls, *args, **kwargs):
if cls.__instance is None:
cls.__instance = object.__new__(cls)
return cls.__instance
else:
return cls.__instance
def __init__(self, book):
self.book = book
def pr(self):
print(self.book)
if __name__ == "__main__":
b = A("wind")
a = A("good")
print(a is b)
print(a.pr())
print(b.pr())
the result is
True
good
None
good
None
why the result is not:
True
wind
good
where is wrong with the code?
python singleton
the code is in belows:
class A(object):
__instance = None
def __new__(cls, *args, **kwargs):
if cls.__instance is None:
cls.__instance = object.__new__(cls)
return cls.__instance
else:
return cls.__instance
def __init__(self, book):
self.book = book
def pr(self):
print(self.book)
if __name__ == "__main__":
b = A("wind")
a = A("good")
print(a is b)
print(a.pr())
print(b.pr())
the result is
True
good
None
good
None
why the result is not:
True
wind
good
where is wrong with the code?
python singleton
python singleton
edited Nov 23 at 2:57
asked Nov 23 at 2:43
littlely
216313
216313
Ita
isb
how shouldpr()
return different values?
– Klaus D.
Nov 23 at 2:51
The wind is the first instance. Why it notTrue wind wind
,
– littlely
Nov 23 at 2:56
add a comment |
Ita
isb
how shouldpr()
return different values?
– Klaus D.
Nov 23 at 2:51
The wind is the first instance. Why it notTrue wind wind
,
– littlely
Nov 23 at 2:56
It
a
is b
how should pr()
return different values?– Klaus D.
Nov 23 at 2:51
It
a
is b
how should pr()
return different values?– Klaus D.
Nov 23 at 2:51
The wind is the first instance. Why it not
True wind wind
,– littlely
Nov 23 at 2:56
The wind is the first instance. Why it not
True wind wind
,– littlely
Nov 23 at 2:56
add a comment |
1 Answer
1
active
oldest
votes
for each time of call A()
, its __init__
will be invoked, as it is a singleton, the __init__()
method invoked twice on the same object.
you could get your expected result with:
b = A("wind")
b.pr()
a = A("good")
a.pr()
print(a is b)
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
for each time of call A()
, its __init__
will be invoked, as it is a singleton, the __init__()
method invoked twice on the same object.
you could get your expected result with:
b = A("wind")
b.pr()
a = A("good")
a.pr()
print(a is b)
add a comment |
for each time of call A()
, its __init__
will be invoked, as it is a singleton, the __init__()
method invoked twice on the same object.
you could get your expected result with:
b = A("wind")
b.pr()
a = A("good")
a.pr()
print(a is b)
add a comment |
for each time of call A()
, its __init__
will be invoked, as it is a singleton, the __init__()
method invoked twice on the same object.
you could get your expected result with:
b = A("wind")
b.pr()
a = A("good")
a.pr()
print(a is b)
for each time of call A()
, its __init__
will be invoked, as it is a singleton, the __init__()
method invoked twice on the same object.
you could get your expected result with:
b = A("wind")
b.pr()
a = A("good")
a.pr()
print(a is b)
answered Nov 23 at 3:57
georgexsh
10.1k11136
10.1k11136
add a comment |
add a comment |
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It
a
isb
how shouldpr()
return different values?– Klaus D.
Nov 23 at 2:51
The wind is the first instance. Why it not
True wind wind
,– littlely
Nov 23 at 2:56