CODEWITHSUNDEEP
python
alphanumeric
alphanumeric

Reputation: 19349

Why One Liner Result Is Different

While working with Fibonacci sequence:

a = 1
b = 3
a, b = b, a + b
print a, b

This properly results to a = 3 and b = 4

Now if I would re-code it as:

a = 1
b = 3
a = b
b = a + b
print a, b

the resulting variable b is 6 instead of 4.

What happens "behind of scenes" when one-liner a, b = b, a + b is used?

Upvotes: 0

Views: 90

Answers (3)

C Panda
C Panda

Reputation: 3415

( ) don't make the sequence a tuple, rather ,s do.

a, b = b, a + b # => (a,b) = (a, a+b) if written with brackets

So, it's standard tuple unpacking. But the thing with names a and b on the lest is they are names of different objects now, namely those known as b and result of a+b previously. This behavior is partly due to the fact that variable names in python are names, not boxes,like in C, that store values.

Upvotes: 0

Gabriel
Gabriel

Reputation: 1942

You said b = 3 and then a = b and then b = a + b which is the same as b = b + b or, in other words, b = 3 + 3, so b = 6.

The first one is like a, b = 3, 1 + 3 or a, b = 3, 4 so b = 4.

Upvotes: 0

Niklas B.
Niklas B.

Reputation: 95328

This is a combination of tuple packing and sequence unpacking. It is parsed the same way as

(a, b) = (b, a + b)

The tuple on the right side is evaluated before the assignment, which is why the "old" values are used.

Upvotes: 6

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