Replacing a file while preserving the previous version

We can leverage the power of pathlib to support a variety of filename manipulations. In the Using pathlib to work with filenames recipe, earlier in this chapter, we looked at a few of the most common techniques for managing directories, filenames, and file suffixes.

One common file processing requirement is to create output files in a fail-safe manner. That is, the application should preserve any previous output file, no matter how or where the application fails.

Consider the following scenario:

1. At time t₀, there's a valid output.csv file from the previous run of the long_complex.py application.
2. At time t₁, we start running the long_complex.py application. It begins overwriting the output.csv file. Until the program finishes, the bytes are unusable.
3. At time t₂, the application crashes. The partial output.csv file is useless. Worse, the valid file from time t₀ is not available either since it...