Start with this great guy https://en.wikipedia.org/wiki/Alonzo_Church

ok

This code was probably written in Python 2.

it should return a filter object, not a list. Need to use list()

great approach

I like lambdas, they make code shorter and look nice. But isn't it against PEP to use lambda function where list comprehension can be used?

I am a Python begineer. Where can I learn Lambda functions in detail?

rather "iterators" than "iterables", iirc, for py3

Oh now I understand, thanks!

I think your int-str conversion is useless.

What filter does is filtering out the items which do not satisfy the prerequisite(the lambda) in a.

The process is:
filter picks the items in a one by one and tests them by the lambda expression.
Each time, lambda accepts one item and returns a boolean value, filter will keeps down the item if lambda returns True or drops it while False.

The items returned from filter are picked from a directly(but not returned by lambda) and the lambda expression should always returns boolean value.

Your solution is so much simpler. Mine had to be so unpythonic because I hadn't known that 'if' needn't be added to the lambda function. The 'else' is mandatory with a linear 'if'. The filter function returns each true value returned by the lambda, and since 0 evaluates to false, I had to convert it to a string a back again. This remained the case even when I swapped 'else 0' for 'else False'.

What eludes me is how 'lambda i: i not in b' does not count 0 as a false value, while the same with the if statement does.