convert matrix to vector python

hello i want to know how can we convert a matrix to a vector in python?

in matlab if i have a matrix a =  [[1 2 3];[4,5,6];[7,8,9]]
if i use a(:)
i will get :1
it's not working in python!!!
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This will work, if I understand correctly that you want to flatten a list of lists:

>>> a=[[1,2,3],[4,5,6],[7,8,9]]
>>> reduce(list.__add__,a)
[1, 2, 3, 4, 5, 6, 7, 8, 9]

dadadudeAuthor Commented:
Actually i want to convert a 2D matrix into a vector:
your example worked but I was wondering if i can do that with numpy.
because later i have to calculate a - 1.
and it's not working with that method.
b = a.flatten(1)
The syntax is actually:
a.flatten(order='C') to order by rows (C style)
a.flatten(order='F') to order by columns (Fortran style), same as in Matlab.

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