Managing square brackets in dictionary keys with dpath library

June 19, 2023

Using the dpath library, I’m having trouble working with a dictionary with keys containing square brackets. From the docs I see that square brackets are considered as elements of regular exporessions. However, this is causing the issue in my case, because I just want them to be "normal" square brackets.

I tried to escape the square brackets with a backspace \[, but the result is the same.

Code example

import dpath

d = {'Position': {'Position x [mm]': 3}}
dpath.search(d, 'Position/Position x [mm]/*')

This outputs: {} instead of the expected {'Position': {'Position x [mm]': 3}}

Maybe there is already a solution for the problem, but I did not find it in the docs.

>Solution :

It seems like dpath uses fnmatch.fnmatch standard library under the hood. As per the documentation,

For a literal match, wrap the meta-characters in brackets. For
example, ‘[?]‘ matches the character ‘?‘

So you have to replace the [ with [[] and ] with []] to get the expected match result.

>>> import dpath
>>> 
>>> d = {'Position': {'Position x [mm]': 3}}
>>> dpath.search(d, 'Position/Position x [[]mm[]]')
{'Position': {'Position x [mm]': 3}}