Help ! newbie problem

[ferdydurke]

hi,

I am trying to learn python... I can't explain the difference beetween these
two programms, Fibonacci suites :

.... print b,
.... a,b,c = b,a+b,c+1
....
1 2 3 5 8 13 21 34 55 89 144

and
.... print b,
.... a=b
.... b=a+b
.... c=c+1
....
1 2 4 8 16 32 64 128 256 512 1024


how about the instructions on the same block ? I thought they could be on
the other lines... perhaps I don't understand a=b and b=a+b ?


thanks in advance.

 

[Rene Pijlman]

ferdydurke:

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

b is set to a + b.

[...]

... a=b
... b=a+b

^
This a has a different value now, because of the previous statement.
So this sets b to b + b.

 

[ferdydurke]

ferdydurke:

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

b is set to a + b.

[...]

... a=b
... b=a+b

^
This a has a different value now, because of the previous statement.
So this sets b to b + b.

thanks a lot for the reply, I gotcha now

 

[Raymond Hettinger]

I am trying to learn python... I can't explain the difference beetween these

two programms, Fibonacci suites :


... print b,
... a,b,c = b,a+b,c+1
...
1 2 3 5 8 13 21 34 55 89 144

and

... print b,
... a=b
... b=a+b
... c=c+1
...
1 2 4 8 16 32 64 128 256 512 1024

In the first program, the each element on the right hand side of the
equal sign is evaluated before any assignments are made. So, the
value of "a" is updated *after* "a+b" is computed.

In the second program, "a" is updated *before* "a+b" is computed.

So, the first program can be expanded to something like this:
.... print b,
.... tmp1 = b
.... tmp2 = a+b
.... tmp3 = c+1
.... a = tmp1
.... b = tmp2
.... c = tmp3


Raymond Hettinger