ObjectPath (Python)

Common errors

• NameError: name 'Tree' is not defined

  cause The Tree class was used without being imported from the objectpath library.
  fix Add `from objectpath import Tree` at the beginning of your script.

• TypeError: 'generator' object is not subscriptable

  cause Attempting to access elements by index (e.g., `results[0]`) directly on the generator returned by `tree.execute()`.
  fix Convert the generator to a list or tuple first: `results = list(tree.execute('$.path'))`.

• SyntaxError: invalid syntax (in query string)

  cause The ObjectPath query string contains a syntax error, which could be due to incorrect operators, malformed expressions, or improper use of built-in functions.
  fix Double-check the query against the ObjectPath reference documentation for correct syntax. Pay attention to quotation marks for string literals, array filtering conditions, and operator precedence.

Warnings

• breaking The primary Python `objectpath` library (version 0.6.1) is not actively maintained. The author has stated that they 'don't code in Python anymore' and cannot accept pull requests. Consider `objectpath-ng` for a potentially more actively maintained alternative if long-term support is critical.
  Fix: For new projects, evaluate alternatives like `objectpath-ng` (installable via `pip install objectpath-ng`) or other modern JSON querying libraries. If continuing with `objectpath`, be aware of the lack of ongoing support for bug fixes or new features.
• gotcha When executing queries, `tree.execute()` returns a generator. If you need a list of all results, you must explicitly convert it (e.g., `list(tree.execute(...))`). Forgetting this can lead to unexpected behavior if you expect an iterable that can be traversed multiple times or directly indexed.
  Fix: Always convert the generator to a list, tuple, or iterate over it directly if you need to consume all results or reuse the collection. Example: `results = list(tree.execute('$.path'))`.
• gotcha ObjectPath uses a custom query syntax that, while powerful, can be unfamiliar to users accustomed to other query languages like XPath or JSONPath, leading to syntax errors or incorrect results. Pay close attention to the documentation for operators and functions.
  Fix: Refer to the ObjectPath Reference documentation for detailed syntax and operator usage. Test complex queries thoroughly with sample data.

Install

• pip install objectpath Install stable version

Imports

• Tree

  from objectpath import Tree

• * (all)

  from objectpath import *

  Imports Tree and other utility functions directly into the namespace.

Quickstart

This quickstart demonstrates how to create an ObjectPath Tree from a JSON-like Python dictionary and execute basic queries to extract data. It shows how to retrieve all authors, filter books by price, and access specific nested properties.

import json
from objectpath import Tree

data = {
    "store": {
        "book": [
            {"category": "reference", "author": "Nigel Rees", "title": "Sayings of the Century", "price": 8.95},
            {"category": "fiction", "author": "E.B. White", "title": "Charlotte's Web", "price": 7.99},
            {"category": "fiction", "author": "J.R.R. Tolkien", "title": "The Lord of the Rings", "isbn": "0-395-19395-8", "price": 22.99}
        ],
        "bicycle": {"color": "red", "price": 19.95}
    }
}

tree = Tree(data)

# Find all authors
authors = tree.execute("$.store.book[*].author")
print(f"Authors: {list(authors)}")

# Find books cheaper than 10
cheap_books = tree.execute("$.store.book[(@.price < 10)].title")
print(f"Cheap books: {list(cheap_books)}")

# Find the red bicycle's price
bicycle_price = tree.execute("$.store.bicycle.price")
print(f"Bicycle price: {bicycle_price}")