CODEWITHSUNDEEP
python
Laura
Laura

Reputation: 1445

In line variables in Python 3

Can someone explain the difference between:

a, b = 0, 1
while b < 10:
    print(b)
    a, b = b, a+b

and

a, b = 0, 1
while b < 10:
    print(b)
    a = b
    b = a+b

Upvotes: 2

Views: 74

Answers (3)

tripleee
tripleee

Reputation: 189809

It's a shorthand to avoid a temporary variable. In many traditional languages, you had to do

tmp = a
a = b
b = b + tmp

Upvotes: 1

Amadan
Amadan

Reputation: 198476

Simultaneous:

a = 1
b = 3
a, b = b, a+b
# a: 3; b: 1+3

Sequential:

a = 1
b = 3
a = b
# a: 3; b: 3
b = a+b
# a: 3; b: 3+3

Upvotes: 3

Cyphase
Cyphase

Reputation: 12022

The first one computes all the new values before updating a and b. The second one computes and updates a before computing and updating b. The second one will give incorrect results because of that.

Here's part of a good talk by Raymond Hettinger where he talks about updating multiple state variables at once.

Upvotes: 2

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