Repeatable pydov sessions

Pydov can be used to integrate DOV data in your own scripts and analysis. By default it will execute a new search operation on every run, making it easy to rerun your analysis at a later time using the latest data that might not have been available before. This means your script and analysis will be reproducible.

For some projects or use-cases one might want to go a step further and want full repeatability: when rerunning the script or analysis exactly the same results should be returned. Pydov supports this too, by allowing users to save (record) a pydov session into an archive and replaying it afterwards.

This could for instance be used to record a session in the initial stage of your research, and replay it from then on to always work with exactly the same dataset. You can make modifications to the analysis parts of your script, as long as the pydov calls remain the same it will be possible to replay the saved archive. The advantage of this approach over another way or form of saving the pydov dataframes is that the code to request the data remains in your script, and it also enables rerunning the entire analysis with updated data simply by removing the replay hook.

It can also be used at the end of your research, to save a repeatable copy of your analysis to disk for archiving purposes. This way, you can be sure it is reproducible and repeatable, no matter what happens to the data in DOV.

Lastly, it could be used to share a session between collegues, students or tutors/mentors. It enables them to rerun your session exactly as you saw it, while also allowing them to both inspect the code and make changes to the analysis part.

Recording a pydov session

To record a pydov session, you can add the following to the top of your script. It will add an instance of the RepeatableLogRecorder to the pydov hooks, which takes a single argument with the directory where the archive will be saved.

import pydov
from pydov.util.hooks import RepeatableLogRecorder


When running your script, pydov will now create a new zip archive in the provided directory and save the entire session inside, including all metadata and search query responses, XML data and even pydov itself.

The archive will also contain a metadata.json file with some more details, including the versions of key dependencies that were installed at the time of recording. Also the timestamp of the recording is added:

    "versions": {
        "pydov": "2.2.0",
        "owslib": "0.25.0",
        "pandas": "1.5.0rc0",
        "numpy": "1.23.1",
        "requests": "2.28.1",
        "fiona": "1.8.21",
        "geopandas": "0.11.1"
    "timings": {
        "start": "20221006T152244",
        "end": "20221006T152246",
        "run_time_secs": 2.0412390239944216

After the script is finished, it will print the location of the archive containing the saved session.

Replaying a saved pydov session

To replay a recorded session, you can add the following to the top of your script. It will prepend the saved session to your Python path, which makes sure the next import(s) of pydov will import from the recorded archive. Next it installs the RepeatableLogReplayer hook, which takes a single argument with the location of the archive.

import sys
sys.path.insert(0, './')

import pydov
from pydov.util.hooks import RepeatableLogReplayer


Distribute this modified version of your script together with the pydov archive, executing it will now always yield the same results.

Note: in order to have full reproducible runs it is advised to also install the same versions of pydov’s dependencies as were used when recording. These version numbers can be found in the metadata.json file inside the archive.