Variable assignment in expressions

Question

Here is my code to generate values in the fibonnacci sequence below 10,000,000.

  3 fibs = [1,1]
  4 while((x = fibs[-1] + fibs[-2]) <= 10000000):
  5             


        

Answer 1

Basically:

fibs = [1]
x = 1

while(x <= 10000000):
  fibs.append(x)
  # It is not possible for "fibs" not to have
  # at least two elements by now
  x = fibs[-1] + fibs[-2]

(It was, in fact, one of the design goals of Python to avoid mixing expressions and assignments like C — that's why there's no x++, x--, which is also a semi-FAQ.)

Answer 2

The reason for not allowing assignment in Python expressions is a common, hard-to-find bug in those other languages, caused by this construct.

Please check http://effbot.org/pyfaq/why-can-t-i-use-an-assignment-in-an-expression.htm

Answer 3

from functools import partial
from itertools import imap, islice, takewhile
import operator
fibs = [1, 1]
for x in takewhile(partial(operator.ge, 10000000),
                   imap(operator.add, fibs, islice(fibs, 1, None))):
    fibs.append(x)

Oh wait, you said "simplest"? Nevermind then.

Answer 4

In Python, assignment is not an expression, and therefore has no value.

The simplest solution is to do the assignment in the first part of the loop:

fibs=[1,1]
while fibs[-1] <= 10000000:
   fibs.append(fibs[-1] + fibs[-2])