Python Forum

>>> flist = []
>>> for i in range(3):
...     flist.append(lambda: i)
...
>>> [f() for f in flist]   # what will this print out?

Why is the above output [2,2,2]?

Thanks,

L

Python uses "late binding" here. Lambda is defined with variable i, but actual value of i is looked up when that lambda is called. After for loop i is 2, so all lambdas return 2.

Common trick to avoid this is to use such variable as another parameter:

lambda x, i=i : x + i  # <- this binds i to actual value of i

In your case lambda i=i : i would work as "expected".