Question

I want to store the intermediate values of a variable in Python. This variable is updated in a loop. When I try to do this with a list.append command, it updates every value in the list with the new value of the variable. How should I do it?

while (step < maxstep):
    for i in range(100):
        x = a*b*c
        f1 += x
    f2.append(f1)
    print f2
    raw_input('<<')
    step += 1

Expected output

[array([-2.03,-4.13])]
<<
[array([-2.03,-4.13]),array([-3.14,-5.34])]

Printed output

[array([-2.03,-4.13])]
<<
[array([-3.14,-5.34]),array([-3.14,-5.34])]

Is there a different way of getting what I want in Python?

Answer 1

Assuming the original had a typo and f1 is actually fi (or vice versa):

fi is a pointer to an object, so you keep appending the same pointer. When you use fi += x, you are actually changing the value of the object to which fi points.

To solve the issue you can use fi = fi + x instead.