CODEWITHSUNDEEP
pythonpython-3.x
cyborg
cyborg

Reputation: 878

Fibonacci series in python giving odd results

I have started learning python and my first program on fibonacci started giving me some weird answer, I know I am missing conceptually something so need guide from some expert on this. My program looks like this

#! usr/bin/python
a,b = 0, 1
while (b < 50):
    print(b)
    a = b
    b = a + b

output

1
2
4
8
16
32

But When i wrote like this I got correct result

#! usr/bin/python
a,b = 0, 1
while (b < 50):
    print(b)
    a,b = b, a + b

output:

1
1
2
3
5
8
13
21
34

Guide me pls

Upvotes: 2

Views: 70

Answers (1)

paxdiablo
paxdiablo

Reputation: 882786

a,b = 0,1
a = b          # a <- 1
b = a + b      # b <- a + b (1 + 1 = 2)

That's two separate operations where the a in the final line has already been modified before use.

On the other hand:

a,b = b, a + b

is an atomic operation where everything on the right side of = is the original value.

Hence it's equivalent to:

a,b = 0,1
t = a          # t <- 0
a = b          # a <- 1
b = t + b      # b <- t + b (0 + 1 = 1)

Upvotes: 6

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