python - Incorrect List manipulation -


let's 

>>> = [1,2,3,4,5]

and want output like

>>> b [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5]]

here code:

class child(object):     def get_lines(self):         = [1,2,3,4,5]                       b=[]         c=[]         j=0         in a:             print             b.append(i)             print b             c.insert(j,b)              j=j+1         print c   son= child() son.get_lines()

when print list b in loop, gives:

1  [1]  2  [1, 2] 3   [1, 2, 3]   4   [1, 2, 3, 4]  5  [1, 2, 3, 4, 5]

and output is:

[[1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5]]

where make wrong in code?

b always same list object (note i've changed print c return c):

>>> map(id, child().get_lines()) ... [49021616, 49021616, 49021616, 49021616, 49021616]

c contains 5 references same list. think want is:

class child(object):      def get_lines(self):         = [1, 2, 3, 4, 5]                       return [a[:x+1] x in range(len(a))]

this makes shallow copy of part (or all) of a each step:

>>> child().get_lines() [[1], [1, 2], [1, 2, 3], [1, 2, 3, 4], [1, 2, 3, 4, 5]]

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