Practical Programming, 3rd Edition

Writing Example Calls Using StringIO

In order to follow the function design recipe, we need to write example calls. Writing these calls using real files would involve creating test files for each of the situations you want to demonstrate. This is fragile, because it means that you can’t just give the program to someone—you need to remember to include the test files in case they want to try your function, and it’s also not optimal because anyone trying to understand the function needs to open the input and output files.

Python provides a class, StringIO, in module io, that can be used as a mock open file. That means that you can read from it using the regular file-reading techniques as if it were a real file. StringIO objects can be used anywhere ...