Python modules for parsing JSON, TOML, YAML, and similar formats produce simple tree structures composed of numbers, strings, Booleans, arrays, and dictionaries. These structures are then parsed for the second time to produce more Pythonic data structures. This usually involves validation of some kind.

We firmly believe that parsing and validation should not be separate steps: structure of data should have a single source of truth (doing otherwise opens door to security issues). Also, existing formal descriptions of syntax (e.g., JSON schema) are too weak for many purposes and unwieldy for others.

Enters the forestwalker. A Python module that makes it easy to traverse trees, parse values while checking types, and report invalid data with their precise location in the tree.

The Forest Walker was written by Martin Mareš mj@ucw.cz. It can be freely used and distributed under the MIT License.