jsonshift 1.3.0

A deterministic JSON payload mapper that transforms source data into target structures using dotted paths, indices and wildcards.

✨ jsonshift

A lightweight Python package to convert one JSON payload into another using a declarative mapping spec defined in JSON.

Designed for deterministic system integrations, data pipelines, and API adapters.

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⚙️ Engine rules

• If the source path does not exist → raises MappingMissingError (unless optional: true is set)

• If the source value is null / None → the destination receives None (defaults do NOT override None)

• defaults only fill values when the destination field is absent (never overwrite existing values or None)

• Supports:

  • dotted paths
  • indexed paths ([0])
  • wildcard paths ([*])
  • automatic list creation
  • infinite nesting depth

• Supports optional mappings using optional: true

• Supports dynamic defaults:

  • { "$now": "date" }
  • { "$now": "datetime" }
  • { "$now": "time" }
  • { "$concat": [...] }
  • { "$upper": ... }
  • { "$lower": ... }
  • { "$capitalize": ... }
  • { "$title": ... }
  • { "$format": { "template": "...", "args": {...} } }

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🧩 Installation

pip install jsonshift
# or for development:
pip install -e .[dev]

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🚀 Complex example (Python)

from jsonshift import Mapper

payload = {
    "customer_name": "John Doe",
    "cpf": "12345678901",
    "email": "[e-mail]",
    "amount": 1500.0,
    "installments": 6,
    "products": [
        {"id": "P-001", "name": "Notebook", "price": 4500.0},
        {"id": "P-002", "name": "Mouse", "price": 250.0}
    ]
}

spec = {
    "map": {
        "customer.name": "customer_name",
        "customer.cpf": "cpf",
        "customer.email": {
            "path": "email",
            "optional": True
        },

        "contract.amount": "amount",
        "contract.installments": "installments",

        "contract.products[*].code": "products[*].id",
        "contract.products[*].title": "products[*].name",
        "contract.products[*].price": "products[*].price",

        "contract.main_product[0].code": "products[0].id",
        "contract.main_product[0].title": "products[0].name"
    },

    "defaults": {
        "contract.type": "CCB",
        "contract.origin": "ORQ",

        "contract.created_date": {"$now": "date"},
        "contract.created_at": {"$now": "datetime"},
        "contract.created_time": {"$now": "time"},

        "contract.products[*].currency": "BRL"
    }
}

out = Mapper().transform(spec, payload)
print(out)

Output (example):

{
  "customer": {
    "name": "John Doe",
    "cpf": "12345678901",
    "email": "[e-mail]"
  },
  "contract": {
    "amount": 1500.0,
    "installments": 6,
    "type": "CCB",
    "origin": "ORQ",
    "created_date": "2025-01-08",
    "created_at": "2025-01-08T12:00:00",
    "created_time": "12:00:00",
    "products": [
      {
        "code": "P-001",
        "title": "Notebook",
        "price": 4500.0,
        "currency": "BRL"
      },
      {
        "code": "P-002",
        "title": "Mouse",
        "price": 250.0,
        "currency": "BRL"
      }
    ],
    "main_product": [
      {
        "code": "P-001",
        "title": "Notebook"
      }
    ]
  }
}

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🧠 Dynamic string defaults

In addition to static values and $now, jsonshift supports dynamic string functions inside defaults.

These functions allow composing and transforming values from literals and payload fields in a deterministic and explicit way.

---

🔹 $concat

Concatenates string literals and payload values.

{
  "defaults": {
    "user.code": {
      "$concat": [
        "USR-",
        { "$path": "id" }
      ]
    }
  }
}

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🔹 $upper / $lower

Transforms strings to upper or lower case.

{
  "defaults": {
    "name_upper": {
      "$upper": { "$path": "name" }
    },
    "email_lower": {
      "$lower": { "$path": "email" }
    }
  }
}

---

🔹 $capitalize

Capitalizes the first character of the string.

{
  "defaults": {
    "first_name": {
      "$capitalize": { "$path": "name" }
    }
  }
}

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🔹 $title

Converts the string to title case (first letter of each word).

{
  "defaults": {
    "full_name": {
      "$title": { "$path": "name" }
    }
  }
}

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🔹 $format

Formats strings using Python-style templates.

{
  "defaults": {
    "external_id": {
      "$format": {
        "template": "{id}-{cpf}",
        "args": {
          "id": { "$path": "id" },
          "cpf": { "$path": "cpf" }
        }
      }
    }
  }
}

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📌 Notes

• Dynamic functions are evaluated only inside defaults
• Paths must be explicitly declared using { "$path": "..." }
• Missing paths raise MappingMissingError
• If any resolved value is None, the result is None
• Dynamic defaults never override existing values or None

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🖥️ Command-line interface (CLI)

Using the same example from examples/:

jsonshift --spec examples/spec.json --input examples/payload.json

Or via stdin:

cat examples/payload.json | jsonshift --spec examples/spec.json

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🧪 Testing

pytest -v

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📄 License

MIT © 2025 Pedro Marques