Question

Given this snippet of code:

funcs = []
for x in range(3):
    funcs.append(lambda: x)
print [f() for f in funcs]

I would expect it to print [0, 1, 2], but instead it prints [2, 2, 2]. Is there something fundamental I’m missing about how lambdas work with scope?

Answer 1

This is a frequent question in Python. Basically the scoping is such that when f() is called, it will use the current value of x, not the value of x at the time the lambda is formed. There is a standard workaround:

funcs = []
for x in range(10):
funcs.append(lambda x=x: x)
print [f() for f in funcs]

The use of lambda x = x retrieves and saves the current value of x.