This is the code given below.
k = [1, 8, 15]
g = (x for x in k if k.count(x) > 0)
k = [2, 8, 22]
print(list(g))
I am getting the output as [8] but it should be [1,8,15], right? since each element is present at least once.
Any plausible explanation for the answer?
That's a generator expression. It creates a generator, not a tuple.
Exactly one part of a generator expression is evaluated at genexp creation time. It's this part:
g = (x for x in k if k.count(x)>0)
# ^
Everything else, including this part:
g = (x for x in k if k.count(x)>0)
# ^
is evaluated lazily.
That means the k you're looping over is the original k, but the k you're calling count on is the new k.
Here's a trick to see which k uses the original/modified list by printing x and k in the generator expression:
1st k refers to the original list:
>>> k = [1,8,15]
>>> g = (x for x in k if (print(x) == None and k.count(x)>0))
>>> k = [2,8,22]
>>> list(g)
1
8
15
2nd k refers to the modified list:
>>> k = [1,8,15]
>>> g = (x for x in k if (print(k) == None and k.count(x)>0))
>>> k = [2,8,22]
>>> list(g)
[2, 8, 22]
[2, 8, 22]
[2, 8, 22]
Debugging trick similar to Shawn's:
def p(label, x):
print(label, x)
return x
k = [1,8,15]
g = (x for x in p('iterate over', k) if p('count in', k).count(x)>0)
k = [2,8,22]
print('between generator construction and consumption')
list(g)
Output (Try it online!):
iterate over [1, 8, 15]
between generator construction and consumption
count in [2, 8, 22]
count in [2, 8, 22]
count in [2, 8, 22]
Generator is fetch on process memory,work like lazy operator so that happen
"""""for x in [1,8,15]: if [2,8,22].count(x): """" That is how interpreter fetch values.
Refer this tweet for more understand:
https://twitter.com/nedbat/status/1503735148378001410?t=lJLT482Vmt19cBNuP-PAWQ&s=19
https://twitter.com/driscollis/status/1503366898234404866?t=OgCM0E1rzWAEQOOziO9uqA&s=19
#Learning with hope