Introduction to JSON PATH

JSON (JavaScript Object Notation) is a lightweight data-interchange format that’s easy to read, write, parse, and generate. When working with complex JSON—nested objects, arrays, and mixed data types—you need a concise way to extract specific values. Enter JSONPath, a query language inspired by XPath for XML. JSONPath provides a simple, declarative syntax to traverse and filter JSON structures.

In this guide, we’ll explore:

1. Basic JSONPath syntax
2. Common operators and filters
3. Practical Python examples with jsonpath-ng

1. Basic JSONPath Syntax

Consider the following sample JSON document:

{
  "store": {
    "book": [
      { "category": "reference", "author": "Nigel Rees",     "title": "Sayings of the Century",      "price": 8.95 },
      { "category": "fiction",   "author": "Evelyn Waugh",   "title": "Sword of Honour",            "price": 12.99 },
      { "category": "fiction",   "author": "Herman Melville","title": "Moby Dick",                  "isbn": "0-553-21311-3", "price": 8.99 },
      { "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 }
  }
}

Key JSONPath tokens:

• $ : the root object
• . or [] : child access
• * : wildcard match (all elements)
• .. : recursive descent

Examples:

• $.store.book
  → Returns the array of all books.
• $.store.book[0].author
  → "Nigel Rees"
• $..price
  → All price values in the document.
• $.store.book[?(@.price < 10)]
  → Books with a price less than 10.

2. Common Operators and Filters

JSONPath offers a variety of operators for powerful data selection. Below is a quick reference table:

Filter operators include:

• <, <=, >, >=, ==, !=
• Boolean AND/OR (&&, ||)

3. Python Examples with jsonpath-ng

Follow these steps to query JSON with Python:

1. Install the library:

   pip install jsonpath-ng
   

2. Use the following script:

   import json
   from jsonpath_ng import parse
   
   data = {
       "store": {
           "book": [
               {"category": "reference", "author": "Nigel Rees",      "title": "Sayings of the Century",      "price": 8.95},
               {"category": "fiction",   "author": "Evelyn Waugh",    "title": "Sword of Honour",            "price": 12.99},
               {"category": "fiction",   "author": "Herman Melville","title": "Moby Dick",                  "isbn": "0-553-21311-3", "price": 8.99},
               {"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}
       }
   }
   
   # Parse and evaluate a JSONPath expression
   jsonpath_expr = parse('$.store.book[?(@.price < 10)].title')
   matches = jsonpath_expr.find(data)
   
   # Extract and print titles
   titles = [match.value for match in matches]
   print(titles)
   

   Expected output:

   ['Sayings of the Century', 'Moby Dick']
   

Further Reading and References

• JSONPath Specification
• jsonpath-ng on PyPI
• Kubernetes JSONPath Guide

By mastering JSONPath, you can dramatically simplify data extraction from nested JSON structures—making your scripts cleaner and more maintainable. Give it a try in your next project!