Question

I have the following python code that generates a list of anonymous functions:

basis = [ (lambda x: n*x) for n in [0, 1, 2] ]     
print basis[0](1)

I would have expected it to be equivalent to

basis = [ (lambda x: 0*x), (lambda x: 1*x), (lambda x: 2*x) ]
print basis[0](1)

However, whereas the second snippet prints out 0 which is what I would expect, the first prints 2. What’s wrong with the first snippet of code, and why doesn’t it behave as expected?

Answer 1

You can use a default parameter to create a closure on n

>>> basis = [ (lambda x,n=n: n*x) for n in [0, 1, 2] ]     
>>> print basis[0](1)
0