"Python" (External Evaluation System)

Details

ExternalEvaluate Usage

  • ExternalEvaluate["Python",code] executes a code string in a Python REPL and returns the results as a Wolfram Language expression.
  • ExternalEvaluate["Python""String",code] executes the code string in a Python REPL and does not interpret the results.

Data Types

  • Not all Python built-in types are supported. The supported Python types are:
  • boolTrue|FalseBoolean values
    arrayNumericArrayarrays (from the NumPy library)
    bytearrayByteArraysequence of integers 0-255
    bytesByteArrayimmutable sequence of integers 0-255
    complexComplexcomplex number
    dateDateObjectspecific calendar date
    datetimeDateObjectspecific date with time granularity
    DecimalRealarbitrary-precision real number
    dictionaryAssociationassociation of keys and values
    floatRealreal-valued number
    FractionRationalfraction object from the fractions module
    frozensetListunordered immutable set of unique values
    ImageImageimage (from Python PIL library)
    intIntegerarbitrary-sized integer
    listListsequence of values
    longIntegerarbitrary-sized integer
    NoneNullnull value
    setListunordered set of unique values
    strStringsequence of character values
    tupleListordered sequence of values
  • The precision of a Real returned from a Decimal object is maintained when returned from ExternalEvaluate.
  • Python complex types are required to be real, and so any Complex expression returned from ExternalEvaluate will have real-valued components.

Usage Notes

  • String templates (<**>) can be used to evaluate and insert Wolfram Language expressions into the Python code string.

Examples

open allclose all

Basic Examples  (1)

Evaluate in Python and return the result:

Create a list in Python and return the result:

Type > to get a Python code cell that uses ExternalEvaluate to evaluate:

import math [math.sqrt(i) for i in range(10)]

Create a list with exponentials and logarithms:

[[i,math.exp(i),math.log(i)] for i in range(1,10)]

Create a list with the days of the week:

import calendar [calendar.day_name[i] for i in range(7)]

Scope  (2)

Start a session:

Evaluate a Boolean statement in Python and return the result:

Create a byte array in Python and return its equivalent in the Wolfram Language:

Another way to work with a byte array in Python:

Create a complex number in Python and return the result:

Create a date in Python and return it:

Close the session:

String templates can be used to insert Wolfram Language expressions into Python code

Set two variables:

The expression x^2+y^2 is evaluated in the Wolfram Language, and the result is converted and inserted into the Python code string:

The Python variable 'a' now holds the resulting list:

Close the session:

Introduced in 2018
 (11.3)