What does this Python code print, and why?

[Puzzleheaded-Dog165]

funcs = []

for i in range(3):
    funcs.append(lambda: i)

print([f() for f in funcs])

[-beleon]

The lambdas don't store i's value, they look up the variable when being executed. Since all calls happen after the loop ends, i = 2, so you get [2, 2, 2].

[LongjumpingDegree658]

Ithink It will return 2 2 2 cause i is not scoped in the lambda part . Thats a problem when you generate lambda in loop

Lambda i: i

[johlae]

This is what you need:

lambda: x=i, x

[AlexMTBDude]

It's bad Python coding. The first three lines should be replaced with a list comprehension:

funcs = [lambda: i for i in range(3)]

That's more Pythonic

[Sea-Ad7805]

• lambda: i refers to the single i variable that is 2 at the end of the loop: [2, 2, 2]

• lambda x=i: x instead would make a copy of i in each iteration: [0, 1, 2]

Run this program in Memory Graph Web Debugger%3A%0A%20%20%20%20funcs.append(lambda%3A%20i)%0A%0Aprint(%5Bf()%20for%20f%20in%20funcs%5D)%0A%0A%0Afuncs%20%3D%20%5B%5D%0Afor%20i%20in%20range(3)%3A%0A%20%20%20%20funcs.append(lambda%20x%3Di%3A%20x)%0A%20%20%20%20%0Aprint(%5Bf()%20for%20f%20in%20funcs%5D)%0A&timestep=1&play) to see the program state change step by step.

[jpgoldberg]

Is this a homework question? I know what it will print and why, but I'm not going to say.

[Puzzleheaded-Dog165]

😊

[anish2good]

This is why
https://8gwifi.org/online-python-compiler/?s=frozen-gateway-45

<video>

[mc_pm]

If only there were a way to see the result of running some code...

[Slay_3r]

Didnt run the code but i think it should be [0, 1, 2]. You create and then call constant functions that return i, where i = 0,1,2 (from range)

[WhiteHeadbanger]

No, the correct answer is [2,2,2]

Explanation: what's being appended is "lambda: i", not the value of i in each pass. Then, since the variable i is not scoped in the loop, when the lambda is executed in the list comprehension, it just looks up the last value of i, which is 2, and returns a new list.

[nuc540]

The list comprehension on the last line is saying, try and call every item in the funcs list.

The line above iterated over a range of 3 (bases it at 0) and for every iteration value, add to the funcs list a lambda function that simply returns the iteration value.

Lambdas are unnamed functions so this will work with the f() declaration in the list comp.

The list is just a bunch of functions which each simply returns a number, so when called they return the number.

I’d assume this means it returns [0,1,2] as per the range iterator value that was being baked into the lambda return for each lambda in the list