I like your solution, but hate the readability of your code. Your variable names are not intuitive and make your code confusing to read.
Consider changing "buffer" to "placeValue" or similar, "expected" to "result" or "answer" or similar, and "appendDig" to "digit" or "currentDigit" or similar.

This solution really should be upvoted, it is perfect, simple, and has a very fast execution time!

The execution time of this solution was much faster than my other solution because I used pure math and did not use a String object.

New to lambda expressions, so please bear with me.
How is k passed into the lambda function? What does k represent? It seems to represent the list of words, but how do we know that? More importantly, how does Python know that?