PythonScript policy

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What

The Python Script policy lets you add customized Python functionality to your API proxy flow, especially when the functionality you need is beyond what the Edge out-of-the-box policies provide.

Python language support is provided through Jython version 2.5.2. Third-party libraries you add must be "pure Python" (implemented only in Python). For more on adding libraries, see Resource files.

A Python policy contains no actual code. Instead, a Python policy references a Python resource and defines the Step in the API flow where the Python script executes. You can upload your script through the Management UI proxy editor, or you can include it in the /resources/py directory in API proxies that you develop locally.

Samples

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Script name="Python-1">
        <DisplayName>Python-1</DisplayName>
        <ResourceURL>py://myscript.py</ResourceURL>
</Script>

import base64

username = flow.getVariable("request.formparam.client_id")
password = flow.getVariable("request.formparam.client_secret")

base64string = base64.encodestring('%s:%s' % (username, password))[:-1]
authorization = "Basic "+base64string

flow.setVariable("authorizationParam",authorization)

Element reference

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Script name="Python-1">
    <DisplayName>Python-1</DisplayName>
    <ResourceURL>py://myscript.py</ResourceURL>
    <IncludeURL>py://myscript_dependency.py</IncludeURL>
</Script>

The following table describes attributes that are common to all policy parent elements:

<DisplayName> element

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, natural-language name.

<DisplayName>Policy Display Name</DisplayName>

<ResourceURL> element

This element specifies the main Python file that will execute in the API flow. You can store this file at the API proxy scope (under /apiproxy/resources/py in the API proxy bundle or in the Scripts section of the API proxy editor's Navigator pane), or at the organization or environment scopes for reuse across multiple API proxies, as described in Resource files. Your code can use the objects, methods, and properties of the JavaScript object model.

<ResourceURL>py://myscript.py</ResourceURL>

<IncludeURL> element

Specifies a Python file to be loaded as dependency to the main Python file specified with the <ResourceURL> element. The scripts will be evaluated in the order in which they are listed in the policy.

Include more than one Python dependency resource with additional <IncludeURL> elements.

<IncludeURL>py://myscript_dependency.py</IncludeURL>

Error codes

This section describes the fault codes and error messages that are returned and fault variables that are set by Edge when this policy triggers an error. This information is important to know if you are developing fault rules to handle faults. To learn more, see What you need to know about policy errors and Handling faults.

Runtime errors

These errors can occur when the policy executes.

Deployment errors

These errors can occur when you deploy a proxy containing this policy.

Fault variables

These variables are set when this policy triggers an error at runtime. For more information, see What you need to know about policy errors.

Example error response

{
  "fault": {
    "faultstring": "Execution of SetResponse failed with error: Pythonscript runtime error: "ReferenceError: "status" is not defined.\"",
    "detail": {
      "errorcode": "steps.script.ScriptExecutionFailed"
    }
  }
}

Example fault rule

<FaultRule name="PythonScript Policy Faults">
    <Step>
        <Name>AM-CustomErrorResponse</Name>
        <Condition>(fault.name Matches "ScriptExecutionFailed") </Condition>
    </Step>
    <Condition>(pythonscript.PythonScript-1.failed = true) </Condition>
</FaultRule>

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