We can use the built-in inputfile module to concatenate files while optionally applying filters and transformations to each line, without abusing nested with blocks and for loops.

When using Pandas in production environments for highly-performant tabular data manipulations, we want to get things right. In particular, we would like to avoid the dangers of silent and potentially deadly mechanisms like implicit type conversion.

While type-annotating your Python code, at some stage you might have felt that for a certain object in a given scope, you are not so much interested in its type as you are in its behaviour.

You don't really mind if it's a Duck, a Goose¹, or even a PersonDisguisedAsADuck, you (and your program) only care about its ability to .quack().

What could you do to support static type checking in this case?