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ExpressionJSON (.json)

  • Import and Export support ExpressionJSON.
  • ExpressionJSON provides lossless round-tripping of Wolfram Language expressions to and from JSON.
  • By default, Import and Export use the "JSON" format for files ending in .json, rather than the "ExpressionJSON" format.

Background & Context

    • MIME type: application/json.
    • Data interchange format.
    • ExpressionJSON provides a JSON representation of Wolfram Language expressions.
    • JSON is commonly used in web programming.
    • JSON is an acronym derived from JavaScript Object Notation.
    • JSON is based on a subset of the JavaScript programming language.
    • Plain text format.
    • JSON was developed in 2001.
    • JSON is published as RFC 4627.

Import & Export

  • Import["file","ExpressionJSON"] imports a file that uses the ExpressionJSON format, producing an ordinary Wolfram Language expression.
  • Export["file",expr,"ExpressionJSON"] exports an arbitrary expression to ExpressionJSON.
  • Elements of expressions are represented as follows in ExpressionJSON:
  • "string""'string'" (UTF-8, with JSON escaping)
    True, Falsetrue, false
    Nullnull
    symbol"symbol" (UTF-8)
    f[e1,e2,…,opt1val1,…]["f",e1,e2,…,["Rule",opt1,val1],…]
  • Machine integers are represented literally. Larger integers are represented as "digits".
  • See the following reference pages for full general information:
  • Import, Exportimport from or export to a file
    CloudImport, CloudExportimport from or export to a cloud object
    ImportString, ExportStringimport from or export to a string
    ImportByteArray, ExportByteArrayimport from or export to a byte array

Import Elements

  • General Import elements:
  • "Elements" list of elements and options available in this file
    "Summary"summary of the file
    "Rules"list of rules for all available elements

Options

  • Export options:
  • "Compact"Falsewhether to omit line breaks and tabs
    "NullSymbols"{}a list of symbols to represent as JSON null
    "PrecisionHandling"Truewhether to allow bignums or issue a message
  • "Compact"->n includes line breaks and tabs up to indent level n.

Examples

Basic Examples  (5)

Import a JSON list:

Wolfram Language code: ImportString["[ \"List\", 1, 2, 3 ]", "ExpressionJSON"]

Import a String:

Wolfram Language code: ImportString["\"'abc'\"", "ExpressionJSON"]

Import a Quantity:

Wolfram Language code: ImportString["[ \"Quantity\", 2.45, \"'Meters'\"]", "ExpressionJSON"]

Export an expression to a JSON string:

Wolfram Language code: ExportString[{1, 2, 3}, "ExpressionJSON"]
Wolfram Language code: ExportString[<|"x" -> 1, "y" -> 2, "z" -> 3|>, "ExpressionJSON", "Compact" -> True]

Export a list while converting None to JSON null:

Wolfram Language code: ExportString[{True, None}, "ExpressionJSON", "NullSymbols" -> {None}]

Export a list of numbers of arbitrary precision:

Wolfram Language code: ExportString[ <|"PlanckConstant" -> 6.626070040 * 10 ^ −34, "AvogadroConstant" -> 6.02214 * 10 ^ 23, "Pi" -> N[Pi, 20]|>, "ExpressionJSON"]

Export a list of numbers and issue an error if any of them is not a machine-precision number:

Wolfram Language code: ExportString[<|"PlanckConstant" -> 6.626070040 * 10 ^ −34, "AvogadroConstant" -> 6.02214 * 10 ^ 23, "Pi" -> N[Pi, 20]|>, "ExpressionJSON", "PrecisionHandling" -> False]

Control the output format with "Compact" to limit indentation:

Wolfram Language code: ExportString[<|"x" -> {{1, 2}, {3, 4}}, "y" -> {{Null}}|>, "ExpressionJSON", "Compact" -> 2]