given function takes x , manipulate x such:
>>> x = [5,3,0,0] >>> j = 1 >>> i, xi in enumerate(x): ... if xi == 0: ... x[i] = 1.0/2**j ... j+=1 ... >>> x [5, 3, 0.5, 0.25] and in function:
def f(x): j = 1 i, xi in enumerate(x): if xi == 0: x[i] = 1.0/2**j j+=1 return x i want change lambda function how possible when uses variable not in loop?
without complication of j+=1 , considering j constant this:
j = 1 f = lambda x: [1.0/2**j if xi == 0 else xi i, xi in enumerate(x)] but need j change when if statement made. how can achieved in lambda function?
you make j itertools.count() object; each time call next() on it'll yield next value in sequence:
from itertools import count j = count(1) f = lambda x: [1.0 / 2 ** next(j) if xi == 0 else xi i, xi in enumerate(x)] this works because ever ask next value when x == 0 true.
however, need reset j each time want use lambda. incorporate list comprehension one-element tuple loop over:
f = lambda x: [1.0 / 2 ** next(j) if xi == 0 else xi j in (count(1),) i, xi in enumerate(x)] all not readable. i'd stick def function object instead.
as side note, use or replace .. if xi == 0 else xi expression; xi == 0 makes xi falsey:
f = lambda x: [xi or 1.0 / 2 ** next(j) j in (count(1),) i, xi in enumerate(x)] 
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