Why reinvent the wheel, when Python ships with an already written and tested solution? The 3 lines of code you would write are probably going to miss some corner case.
If I'm reading some unfamiliar code I would rather see one use of a standard library function call than several lines that I have to read and understand. And if it was really the first time I came across the `fileinput` module, I only have to pay the cost of reading the documentation once, and then forever benefit from having to read and understand less code whenever it is used.
