CODEWITHSUNDEEP
python
Mr-Eyes
Mr-Eyes

Reputation: 27

What is the different between these two ways for declaring variables in python?

While printing fibonacci Series

a,b,c=1,1,1
while (c<7):
  print(b,end=" ")
  a,b,c=b,b+1,c+1

the output is >> 1 2 3 5 8 13

and when I was tracing the code I found the result is >> 1 2 4 8 16 32

this output resulted by declaring the variables in this way 

a,b,c=1,1,1
while (c<7):
  print(b,end=" ")
  a=b
  b=a+b
  c=c+1

So what is the difference between these two different ways in declaring the variables

Upvotes: 2

Views: 69

Answers (3)

Eric
Eric

Reputation: 97641

This line:

a,b,c=b,a+b,c+1

is equivalent to:

new_a = b
new_b = a + b
new_c = c + 1

a = new_a
b = new_b
c = new_c

Upvotes: 1

devnull
devnull

Reputation: 123608

The difference is that when you say:

  a,b,c=b,b+1,c+1

the rhs of = is evaluated and then the values are assigned to the variables on the lhs.

This would work ok as long as the assignments do not have a side-effect on the subsequent ones. For example:

a=42
b=7+a
c=b-a

isn't the same as

a, b, c = 42, 7+a, b-a

If a, b, c were all set to 0 then in the first case you'd end up with 42, 49, 7 respectively. Whereas in the second case, you'd get 42, 7, 0

Upvotes: 2

OrangeCube
OrangeCube

Reputation: 398

What's happening in your first example is called "tuple assignment".

Python first constructs the tuple (b, b+1, c+1), and then pairwise assigns each value to its corresponding variable.

it's a more pythonic way for assignment.

Upvotes: 1

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