is this a bug? (python 2.3)

[Sean McIlroy]

hi all

when i run this code in python 2.3

###################### BEGIN CODE
class warfare:
def __init__(self): self.pairs = [[0,0]]*2
def __str__(self): return str(self.pairs)
def setfirst (self,i,value): self.pairs[0] = value
def setsecond(self,i,value): self.pairs[1] = value

w = warfare()
print w
w.setfirst(0,'hello')
print w
###################### END CODE

i get this result

###################### BEGIN ACTUAL RESULT
[[0, 0], [0, 0]]
[['hello', 0], ['hello', 0]]
###################### END ACTUAL RESULT

instead of the expected result

###################### BEGIN EXPECTED RESULT
[[0, 0], [0, 0]]
[['hello', 0], [0, 0]]
###################### END EXPECTED RESULT

is there a reasonable explanation for this behavior?

peace
stm

 

[Carsten Haese]

hi all

when i run this code in python 2.3

###################### BEGIN CODE
class warfare:
def __init__(self): self.pairs = [[0,0]]*2
def __str__(self): return str(self.pairs)
def setfirst (self,i,value): self.pairs[0] = value
def setsecond(self,i,value): self.pairs[1] = value

w = warfare()
print w
w.setfirst(0,'hello')
print w
###################### END CODE

i get this result

###################### BEGIN ACTUAL RESULT
[[0, 0], [0, 0]]
[['hello', 0], ['hello', 0]]
###################### END ACTUAL RESULT

instead of the expected result

###################### BEGIN EXPECTED RESULT
[[0, 0], [0, 0]]
[['hello', 0], [0, 0]]
###################### END EXPECTED RESULT

http://www.python.org/doc/faq/programming/#how-do-i-create-a-multidimensional-list

-Carsten

 

[Sean McIlroy]

thanks

 

[Gabriel Genellina]

class warfare:
def __init__(self): self.pairs = [[0,0]]*2
def __str__(self): return str(self.pairs)
def setfirst (self,i,value): self.pairs[0] = value
def setsecond(self,i,value): self.pairs[1] = value

http://www.python.org/doc/faq/programming/#how-do-i-create-a-multidimensional-list

Also see this more general topic:
http://www.python.org/doc/faq/general/#why-are-default-values-shared-between-objects