The problem I've noticed is that if I append the file with each of the 100k runs (one at a time), it can happen that two threads try to save to the file at the same time and some row(s) end up empty.

How to write to a file in Python with modules. Of course, some files are going to contain more complex formatting than others. For example, if you want to write a .Doc file in Python, you’ll ...

The newly approved Python Enhancement Proposal 751 gives Python a standard lock file format for specifying the dependencies of projects. Here’s the what, why, and when.