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Target release	2.0
Epic
Document status
Document owner	Former user (Deleted)
Designer	Former user (Deleted)
Developers	Former user (Deleted), Marco Peters
QA	Olga Faber (Unlicensed)

Goals

Let Python programmers write GPF operators using CPython and its scientific extension libraries numpy, scipy, pandas, etc.
It should be transparent to users how operators are implemented, e.g. using the native Java GPF API, using the Python API or using the stand-alone tools adapter.

Background and strategic fit

Scientists prefer Python over Java.

Assumptions

Users have Python 2.7, 3.3 or 3.4 installed.

Requirements

#	Title	User Story	Importance	Notes
1	Short identifier for the story	Describe the user and what they are trying to achieve	Must Have	Additional considerations or noteworthy references (links, issues)

User interaction and design

A Python extension module is a JAR file or directory which must contain a plain text file META-INF/snappy.def which lists all Python extensions contained in the module. Python extension modules are found in the following locations:

<module-jar-file> a module JAR file
${user.home}/.snap/snappy/ext/* the directories in directory snappy/ext in the SNAP user directory
${snap.snappy.ext} from the directory paths given in the special system property snap.snappy.ext

The text file snappy.def contains either empty lines, comment lines starting with the '#' character, or lines declaring a Python extension as follows:

[<ext-rel-path>/]<ext> ExtClass

The type of the extension is derived from the Python class ExtClass. If the class name ends with Op it is assumed to be a GPF operator, if it ends with Action it is assumed to be an action to be placed in the menu or in a toolbar. A single <ext> may contain any number of Python classes that provide extensions to SNAP.

Each Python extension must follow this schema:

[<ext-rel-path>/]

<ext>.py the Python code containing the class ExtClass

<ext>-info.xml contains the operator metadata such as processing parameter definitions (for GPF operators only)

Questions

Below is a list of questions to be addressed as a result of this requirements document:

Question	Outcome
(e.g. How we make users more aware of this feature?)	Communicate the decision reached

Not Doing

List the features discussed which are out of scope or might be revisited in a later release.