Why it only realize the last instance when using python singleton pattern
0
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
asked Nov 23 '18 at 2:43
littlelylittlely
299315
add a comment |
0
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
asked Nov 23 '18 at 2:43
littlelylittlely
299315
Itaisbhow shouldpr()return different values?
– Klaus D.
Nov 23 '18 at 2:51
The wind is the first instance. Why it notTrue wind wind,
– littlely
Nov 23 '18 at 2:56
add a comment |
0
0
0
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
asked Nov 23 '18 at 2:43
littlelylittlely
299315
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
asked Nov 23 '18 at 2:43
littlelylittlely
299315
asked Nov 23 '18 at 2:43
littlelylittlely
299315
edited Nov 23 '18 at 2:57
littlely
asked Nov 23 '18 at 2:43
littlelylittlely
299315
asked Nov 23 '18 at 2:43
littlelylittlely
299315
asked Nov 23 '18 at 2:43
littlelylittlely
299315
299315
Itaisbhow shouldpr()return different values?
– Klaus D.
Nov 23 '18 at 2:51
The wind is the first instance. Why it notTrue wind wind,
– littlely
Nov 23 '18 at 2:56
add a comment |
Itaisbhow shouldpr()return different values?
– Klaus D.
Nov 23 '18 at 2:51
The wind is the first instance. Why it notTrue wind wind,
– littlely
Nov 23 '18 at 2:56
It
a is b how should pr() return different values?– Klaus D.
Nov 23 '18 at 2:51
It
a is b how should pr() return different values?– Klaus D.
Nov 23 '18 at 2:51
The wind is the first instance. Why it not
True wind wind,– littlely
Nov 23 '18 at 2:56
The wind is the first instance. Why it not
True wind wind,– littlely
Nov 23 '18 at 2:56
add a comment |
1 Answer
1
active
oldest
votes
2
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 '18 at 3:57
georgexshgeorgexsh
10.8k11339
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
2
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 '18 at 3:57
georgexshgeorgexsh
10.8k11339
add a comment |
2
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 '18 at 3:57
georgexshgeorgexsh
10.8k11339
add a comment |
2
2
2
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 '18 at 3:57
georgexshgeorgexsh
10.8k11339
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 '18 at 3:57
georgexshgeorgexsh
10.8k11339
answered Nov 23 '18 at 3:57
georgexshgeorgexsh
10.8k11339
answered Nov 23 '18 at 3:57
georgexshgeorgexsh
10.8k11339
answered Nov 23 '18 at 3:57
georgexshgeorgexsh
10.8k11339
10.8k11339
add a comment |
add a comment |
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It
aisbhow shouldpr()return different values?– Klaus D.
Nov 23 '18 at 2:51
The wind is the first instance. Why it not
True wind wind,– littlely
Nov 23 '18 at 2:56