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PythonExpression

Background & Context

    • Code representation format for the Python programming language.
    • PythonExpression supports Python numbers, strings, lists, Booleans and dictionaries.
    • Plain text format.
    • Python was first released as a programming language in 1991.

Import & Export

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
  • Details of elements...
  • "Data"the literal Python expression
  • ImportString uses the "Data" element by default.
  • The symbol Null is represented as the Python value "None".
  • Not all Python built-in types are supported. The supported Python types are:
  • tupleListan ordered sequence of values
    dictionaryAssociationan association of keys and values
    intIntegerarbitrary-sized integer
    longIntegerarbitrary-sized integer
    floatRealreal-valued number
    complexComplexa complex number
    listLista sequence of values
    booleanTrue|FalseBoolean values
    stringStringa sequence of character values
    NoneNullnull value

Examples

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Basic Examples  (6)

Import a simple string:

Wolfram Language code: ImportString["'hello world'", "PythonExpression"]

Import a list:

Wolfram Language code: ImportString["[1,'h',True,None,1.2]", "PythonExpression"]

Export to a string:

Wolfram Language code: ExportString[Range[10], "PythonExpression"]

Import a dictionary as a Wolfram Language list:

Wolfram Language code: ImportString["{'a':1,'b':2}", "PythonExpression"]

Export an Association as a Python dictionary:

Wolfram Language code: ExportString[<|"a" -> 1, "b" -> 2|>, "PythonExpression"]

Import the result of evaluating external code in Python:

Wolfram Language code: ImportString[ExternalEvaluate["Python" -> "String", "'hello world'"], "PythonExpression"]

Confirm it is the same as using the "ReturnType" of "Expression":

Wolfram Language code: % == ExternalEvaluate["Python" -> "Expression", "'hello world'"]

Possible Issues  (1)

"PythonExpression" internally starts and stops a Python session every time ImportString is called, which takes a substantial amount of time:

Wolfram Language code: expressions = {"[1, 2, {1:2}]", "1 + 1", "sum(range(10))"};
Wolfram Language code: Map[ ImportString[#, "PythonExpression"] &, expressions ]//RepeatedTiming

When performance is a concern, manually manage a Python session using ExternalEvaluate:

Wolfram Language code: With[ {s = StartExternalSession["Python"]}, WithCleanup[ ExternalEvaluate[s, expressions] // RepeatedTiming, DeleteObject[s] ] ]