eLg - 1 year ago 104

Python Question

I am trying to understand Python, but I still don't get it. I am new to the language, and wants to understand it properly.

This is a line from a Fibonacci sequence using loops. Please explain the meaning of this code. I am trying to get the pattern by hand. I got the pattern up to 3, but after 3 I am not getting the answer.

`a, b = 0, 1`

while b < 50:

print(b)

a, b = b, a + b

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Answer Source

```
a, b = b, a + b
```

This is known as multiple assignment. It's basically an *atomic* version of:

```
a = b
b = a + b
```

By atomic, I mean everything on the right is calculated *before* pacing it into the variables on the left. So `a`

becomes `b`

and `b`

becomes the *old* version of `a`

plus `b`

, equivalent to the non-atomic:

```
old_a = a
a = b
b = old_a + b
```

So, in terms of what you see:

```
a b output
================ ========================= ======
(initial values) (initial values)
0 1 1
(becomes prev b) (becomes sum of prev a,b)
1 1 1
1 2 2
2 3 3
3 5 5
5 8 8
```

That exact code (along with the explanation of multiple assignment) can be found here in the tutorial.

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