Calculate Python Expression

This is a container functor that runs a Python instance with the user-defined expression. Like the other calculator functors, data is connected through hook functors placed inside its {{ … }} block. See also Calculate R Expression for the equivalent functor using R.

Data is passed into the expression through hook functors placed inside the container's {{ … }} block — the same verbose form hook mechanism used by the calculator functors:

• Tables and lookup tables → Number Table → available in the expression as dinamica.inputs[“t1”], dinamica.inputs[“t2”], …, dinamica.inputs[“t100”]
• Scalar values → Number Value → available as dinamica.inputs[“v1”], dinamica.inputs[“v2”], …, dinamica.inputs[“v100”]
• Strings → Number String → available as dinamica.inputs[“s1”], dinamica.inputs[“s2”], …, dinamica.inputs[“s100”]

Maps cannot be connected — this functor has no cell context. There is no shorthand notation. See Calculate Functors — Complete Operator Documentation for the general hook mechanism and syntax.

Every table or lookup table arriving through dinamica.inputs is represented in Python as a list of lists: the first inner list contains the column names (the header row) and every subsequent inner list is a row of data. The header name of each key column has an asterisk (*) appended to it.

Values are returned to Dinamica by assigning them into dinamica.outputs, keyed by the desired output name. Every assigned value becomes an entry in the output result struct:

// Scalar values are assigned directly
dinamica.outputs["patchCount"] = 42
dinamica.outputs["totalArea"] = 1530.5

Tables and lookup tables cannot be assigned directly — they must first be converted using the utilities described below. If a table arriving from an input already carries * markers on its key column names, it can be assigned directly to an output without conversion.

CalculatePythonExpression returns a single Struct value (via its result output port) containing every entry assigned to dinamica.outputs. To retrieve individual values from that struct, use the following functors from the Integration group:

Each functor takes two inputs: the Struct returned by CalculatePythonExpression, and the name of the entry to extract as a string constant. For example, to retrieve a numeric output named patchCount and a table output named filteredPatches:

result := CalculatePythonExpression (String $"(
myTable = [["PatchId*", "Area"], [1, 12.4], [2, 8.7]]
dinamica.outputs['patchCount'] = 42
dinamica.outputs['filteredPatches'] = dinamica.prepareTable(myTable, 1)
)") {{ }};
patchCount      := ExtractStructNumber result "patchCount";
filteredPatches := ExtractStructTable  result "filteredPatches";

Packages can be installed in two ways: calling dinamica.package(…) from within the expression, or listing package names on the packages input port, one per line. The two differ in timing: dinamica.package(…) runs during the expression, so it can be called conditionally; the packages port always runs before the expression executes. Because dinamica.package(…) runs together with the script, it may fail if a package is already loaded in an incompatible version.

dinamica.package(packageName, installPath=None, loadPath=None) installs (if needed via pip) and imports the requested module.

Simply install and load numpy:

dinamica.package("numpy")

Specify a version:

dinamica.package("numpy", "numpy==1.19.5")

Install a package whose importable name differs from its pip name:

dinamica.package("segment_anything_py", "segment_anything_py", "segment_anything")

Use arbitrary pip parameters, such as installing from a remote wheel with a custom index:

dinamica.package("segment_anything_py", "https://files.pythonhosted.org/packages/43/2f/dabe75d90a7eb54a0a609a0fc5c36d1933256319beaea5d6b2f176e213a2/segment_anything_py-1.0-py3-none-any.whl --index-url https://download.pytorch.org/whl/cu118", "segment_anything")

Chain several installs:

dinamica.package("cython")
dinamica.package("numpy")
dinamica.package("pycocotools", "git+https://github.com/philferriere/cocoapi.git#egg=pycocotools&subdirectory=PythonAPI")

The packages port takes one package identifier per line, in any form accepted by pip. It only installs — unlike dinamica.package(), it does not also import the module, and it does not support specifying a separate install name and import name. Every listed package is installed before the expression runs, but the expression must still import each one itself, using its actual importable name (which may differ from the name given to pip):

numpy
requests==2.31.0
torchvision==0.19.1 --index-url https://download.pytorch.org/whl/cu121

import numpy
import requests
import torchvision

Converts a list of lists into a table ready to be assigned to an output. The first inner list must be the header row.

Converts a list of lists into a lookup table ready to be assigned to an output. The first inner list must be the header row.

Converts several Python data shapes into a valid Dinamica table for output.

The following examples use a consistent set of inputs:

• t1 — a table of land cover patches, with columns PatchId*, Area, and CategoryId
• t2 — a lookup table mapping category identifiers to category names
• v1 — a scalar minimum area threshold

Install and import numpy, then inspect all inputs passed in by Dinamica:

dinamica.package("numpy")
print(dinamica.inputs)

Note: The print() call is visible in Dinamica EGO's Message Log, shown as a Result-level message. Log levels are ordered Unconditional, Error, Warning, Result, Info, Info2, Debug, Debug2 — messages printed from Python are only shown when the Message Log level is set to Result or a more verbose level; at Unconditional, Error, or Warning they are suppressed.

Print the rows of both connected tables to verify their contents:

for row in dinamica.inputs["t1"]:
    print(row)

for row in dinamica.inputs["t2"]:
    print(row)

Count the patches whose area meets the minimum threshold and sum their total area:

patchCount = 0
totalArea = 0.0
for row in dinamica.inputs["t1"][1:]:
    if row[1] >= dinamica.inputs["v1"]:
        patchCount += 1
        totalArea += row[1]

dinamica.outputs["patchCount"] = patchCount
dinamica.outputs["totalArea"] = totalArea

Return a filtered table containing only the patches above the threshold:

filtered = [dinamica.inputs["t1"][0]]
for row in dinamica.inputs["t1"][1:]:
    if row[1] >= dinamica.inputs["v1"]:
        filtered.append(row)

dinamica.outputs["filteredPatches"] = dinamica.prepareTable(filtered, 1)

Compute the total area per category and return it as a lookup table:

areaSums = {}
for row in dinamica.inputs["t1"][1:]:
    categoryId = row[2]
    areaSums[categoryId] = areaSums.get(categoryId, 0.0) + row[1]

lut = [["CategoryId*", "TotalArea"]]
for catId, total in areaSums.items():
    lut.append([catId, total])

dinamica.outputs["areaByCategory"] = dinamica.prepareLookupTable(lut)

When writing a script by hand, the expression input cannot be filled in directly as a text constant: the Code type is represented in the underlying script using base64 encoding, which is impractical to write or edit directly. Instead, connect a String carrier functor containing the expression text to the expression port — its output is accepted wherever a Code value is expected. Since only this one output is needed, the carrier can be inlined directly into the call.

This limitation is specific to hand-written EGO Script. In the Dinamica EGO GUI, the expression port has a dedicated code editor that edits the Code value directly — the String carrier workaround is only necessary when writing or editing the .ego file as text.

The following counts the patches in a land cover areas table whose area meets a minimum threshold:

result := CalculatePythonExpression (String $"(
total = 0
for row in dinamica.inputs['t1'][1:]:
    if row[1] >= dinamica.inputs['v1']:
        total += 1
dinamica.outputs['patchCount'] = total
)") {{
    NumberTable landCoverAreas 1;
    NumberValue minimumArea    1;
}};
patchCount := ExtractStructNumber result "patchCount";

CalculatePythonExpression returns a Struct containing all values assigned to dinamica.outputs. The ExtractStructNumber functor then pulls the patchCount entry out of that struct by name. See Retrieving outputs for the full list of extraction functors.

A more involved example: installing numpy to compute area statistics for a land cover patches table and flag outlier patches, then retrieving both the scalar statistics and the resulting table:

result := CalculatePythonExpression (String $"(
dinamica.package('numpy')

areas = numpy.array([row[1] for row in dinamica.inputs['t1'][1:]])

meanArea = float(numpy.mean(areas))
stdArea = float(numpy.std(areas))

isOutlier = numpy.abs(areas - meanArea) > 2 * stdArea

dinamica.outputs['meanArea'] = meanArea
dinamica.outputs['stdArea'] = stdArea

header = dinamica.inputs['t1'][0]
outlierRows = [row for row, flagged in zip(dinamica.inputs['t1'][1:], isOutlier) if flagged]
outlierTable = [header] + outlierRows

dinamica.outputs['outlierPatches'] = dinamica.prepareTable(outlierTable, 1)
)") {{
    NumberTable landCoverPatches 1;
}};
meanArea       := ExtractStructNumber result "meanArea";
stdArea        := ExtractStructNumber result "stdArea";
outlierPatches := ExtractStructTable  result "outlierPatches";

Here landCoverPatches is bound to t1 through a single Number Table hook.

Integration

CalculatePythonExpression