grabmonkey 1.0.0

Dot-path access, mutation, and flattening for deeply nested dict/JSON data, with clear error messages.

grabmonkey

Dot-path access, mutation, and flattening for deeply nested dict/JSON data — with error messages that tell you exactly which level failed.

Stop writing this:

data.get("response", {}).get("results", [{}])[0].get("metadata", {}).get("created_at", "")

Write this:

from grabmonkey import grab

grab(data, "response.results[0].metadata.created_at", default="")

Install

pip install grabmonkey

Requires Python 3.11+. No runtime dependencies.

Quick start

from grabmonkey import grab, grab_many, put, delete, flatten, unflatten

data = {"response": {"results": [{"metadata": {"id": 1, "created_at": "2026"}}]}}

# Read, any depth
grab(data, "response.results[0].metadata.created_at")   # "2026"

# Safe default instead of an exception
grab(data, "response.results[0].missing", default="")   # ""

# Type coercion on access
grab({"count": "42"}, "count", as_type=int)             # 42

# Wildcards over lists
grab({"items": [{"n": 1}, {"n": 2}]}, "items[*].n")     # [1, 2]

# Batch access
grab_many(data, {"id": "response.results[0].metadata.id"})   # {"id": 1}

# Set and delete (mutates in place, creates intermediate containers)
d = {}
put(d, "a.b[2].c", 9)              # {"a": {"b": [None, None, {"c": 9}]}}
delete(d, "a.b[2].c")              # {"a": {"b": [None, None, {}]}}
delete(d, "a.b[2]", prune=True)    # {"a": {"b": [None, None]}}  (prune drops empties)

# Flatten / unflatten
flatten({"a": {"b": [1, 2]}})           # {"a.b[0]": 1, "a.b[1]": 2}
unflatten({"a.b[0]": 1, "a.b[1]": 2})   # {"a": {"b": [1, 2]}}

Clear errors

grab(data, "response.results[0].nope")
# grabmonkey.errors.PathError:
# Path 'response.results[0].nope' failed at 'nope':
# key not found in dict with keys ['metadata']

PathError (a LookupError) means a structural miss — the case default= absorbs. PathSyntaxError means a malformed path string. CoercionError means the value was found but as_type could not convert it. The last two are not absorbed by default=, on purpose.

Path syntax

Syntax	Meaning
a.b.c	dict key or object attribute
items[0], items[-1]	sequence index
items[*]	every element of a sequence / value of a mapping
data['weird.key']	quoted key for keys with dots/brackets/spaces

Works on dicts, lists, dataclasses, named tuples, and any object with attribute access. Strings and bytes are treated as leaf values, not navigable containers (see LIMITATIONS.md).

CLI

Reads JSON from a file (--input) or stdin, prints JSON:

echo '{"user":{"name":"Alice"}}' | grabmonkey grab user.name   # "Alice"
echo '{"a":{"b":1}}'             | grabmonkey flatten          # {"a.b": 1}
grabmonkey grab metadata.id --input response.json

Using with AI assistants

See SKILL.md for an LLM-consumable reference (decision table, worked examples, anti-patterns). See LIMITATIONS.md for deliberate design tradeoffs.

License

MIT