In dask.array we allow user provided functions to get a special keyword, block_info with information about the array and where the block that they're operating in that array lives:

We might consider doing the same for dask.dataframe.map_partitions. We have a bit less information to provide, but can probably include:

1. The number of partitions in the dataframe
2. Which partition we're on specifically

This requires using the dask.base.has_keyword function to inspect the user provided function, and then manipulating the task graph a bit to add the extra keyword argument.

Inspired by this stack overflow question: https://stackoverflow.com/questions/51135739/how-to-modify-values-on-specific-dask-dataframe-partiton