Debugging Transformation Errors

Debug various transformation and library errors.

  •   5 minute read  

This guide lists the different errors you might encounter while using transformations and libraries, and how to fix them.

JavaScript

ReferenceError

This error occurs when a non-existent variable is referenced somewhere in the transformation.

Sample code and errorPossible solution
export function transformEvent(event, metadata) {
   event.someValue = value; 
   return event;
}

Error:
“ReferenceError: value is not defined \n”
at transformEvent (base transformation: 2:25)
Make sure variable is declared and available in the scope. You can also use an optional check:
if(value) {
  event.someValue = value;
}
Library code:
// jslibsub
export function sub(a,b) {
  return a-b-c;
}
Transformation code:
import { sub } from ‘jslibsub’;

export function transformEvent(event, metadata) {
  event.sub = sub(1, 2)
  return event;
}

Error:
ReferenceError: c is not defined
  at sub (library jslibsub:2:14)
  at transformEvent (base transformation:4:17)
Make sure variable is declared and available in the scope.

See Error message format for more context on the error message.

TypeError

This error occurs when a property is read or function is called on an undefined variable.

Sample code and errorPossible solution
export function transformEvent(event, metadata) {
   event[‘val’]=event.context.traits.obj.val1; 
   return event;
}

Error:
“TypeError: Cannot read properties of”
undefined (reading ‘val1’)\n 
at transformEvent (base transformation:2:43)
Use optional chaining when accessing nested fields.
event.val = event.context?.traits?.obj?.val1;

SyntaxError

This error occurs when you run a syntactically invalid code, that is, it does not conform to the language syntax. For example, SyntaxError: Unexpected identifier, SyntaxError: Unexpected token.

Sample code and errorPossible solution
export function transformEvent(event, metadata) {
 returns event; 
}

Error:
SyntaxError: Unexpected identifier
[base transformation:2:13]
Check your code for any misspelt keywords and missing operators/commas.

Expected…Found error

This error occurs when you specify a transformation function other than transformEvent or transformBatch.

Sample code and errorPossible solution
export function transformEvent2(event, metadata) {
   return event; 
}

Error:
Error: Expected one of transformEvent,transformBatch. 
Found
Verify that the transformation function is either transformEvent or transformBatch.

Import error

This error occurs when the module you are tring to import from a library does not exist.

Sample code and errorPossible solution
import {add} from ‘jsLib’; 
export function transformEvent(event, metadata) {
   return event; 
}

Error:
Error: import from jsLib failed. Module not found.
Verify that the module you are trying to import exists in the transformation library.

Python

NameError

This error occurs when when the transformation tries to access or use a variable that has not been defined or assigned a value.

Sample code and errorPossible solution
def transformEvent(event, metadata):
   event[‘some_value’]=value
   return event

Error:
NameError(“name ‘value’ is not defined”)
  at transformEvent (base transformation: line 2)
  event[‘some_value’]=value
Make sure variable is declared and available in the scope. You can also use an optional check:
if(value):
  event.someValue = value;
Library code:
def sub(a, b):
  return a-b-c
Transformation code:
from pylibsub import sub

def transformEvent(event, metadata):
  event[‘sub’] = sub(1,2)
  return event

Error:
NameError("name ‘c’ is not defined")
  at sub (library pylibsub: line 2)
   return a-b-c
  at transformEvent (base transformation: line 4)
  event[‘sub’] = sub(1,2)
Make sure variable is declared and available in the scope.

See Error message format for more context on the error message.

ZeroDivisionError

This error occurs when when the transformation attempts to divide a number by zero.

Sample code and errorPossible solution
def transformEvent(event, metadata):
   event[‘value’]=0/0
   return event

Error:
ZeroDivisionError(‘division by zero’)
   at transformEvent (base transformation: line 2)
   event[‘val’]=0/0
Verify your transformation logic.

KeyError

This error occurs when the transformation attempts to access a dictionary item that does not exist.

Sample code and errorPossible solution
def transformEvent(event, metadata):
   event[‘val’]=event[‘context’][’traits’][‘obj’][‘val1’]
   return event

Error:
KeyError(‘obj’)
   at transformEvent (base transformation: line 2)
   event[‘val’]=event [‘context’][’traits’][‘obj’][‘val1’]
Verify the key that transformation is attempting to access exists in the dictionary. You can also set a optional chaining event like:
event[‘val’] = event.get(‘context’).get(
‘traits’,{}).get(‘obj’, {}).get(‘val1’)

BadCodeError

This error occurs when the transformation contains syntactically invalid code or is trying to import an unsupported module/package.

Sample code and errorPossible solution
def transformEvent(event, metadata):
   returns event

Error:
BadCodeError(‘invalid syntax (, line 2)’)
Verify the syntax of your transformation code.
from pyLib2 import add
def transformEvent(event, metadata):
   return event

Error:
BadCodeError(“Unpermitted import(s). Supported modules /
packages for import: {‘sampleTransformationLibrary’,
‘time’, ‘random’, ‘base64’, ‘string’, ‘dateutil’,
‘hashlib’, ‘uuid’, ‘urllib’, ’re’, ‘rudderEmail’,
‘json’, ‘collections’, ‘datetime’, ‘ast’, ‘requests’,
‘math’, ‘user_transformation’, ‘hmac’}”)
Verify that the library imports one of the supported built-in packages and user-written libraries only.

Exception error

This error occurs when you specify a transformation function other than transformEvent or transformBatch.

Sample code and errorPossible solution
def transformEvent2(event, metadata):
   return event

Error:
Exception(“Expected one of [’transformEvent’, ’transformBatch’].
Found []”)
Verify that the transformation function is either transformEvent or transformBatch.

ImportError

This error occurs when the module you are tring to import from a library does not exist or is not found.

Sample code and errorPossible solution
from pyLib1 import adds
def transformEvent(event, metadata):
   return event

Error:
ImportError(“cannot import name ‘adds’ 
from ‘pyLib1’ <redacted_path_to_pyLib1>”)
Verify that the module you are trying to import exists in the transformation library.

Error message format

Standalone transformation

A typical JavaScript transformation error is shown:

ReferenceError: c is not defined
    at sub (library jssublib:2:14)
    at transformEvent (base transformation:4:22)

You can interpret the above error as follows:

  • ReferenceError: c is not defined: The actual error message.
  • at sub (library jssublib:2:14): Module in which the error occurs (line: position).
  • at transformEvent (base transformation:4:22): Depicts where the module is referenced in the transformation (line: position).

Transformation referencing a library

A typical Python transformation error is shown:

NameError(\"name 'c' is not defined\")
    at sub (library pylibsub: line 2)
    return a-b-c
    at transformEvent (base transformation: line 4)
    event['sub'] = sub(1,2)

You can interpret the above error as follows:

  • NameError("name 'c' is not defined"): The actual error message.
  • at sub (library pylibsub: line 2): Line at which error occurred in the library.
  • return a-b-c: Line where the error occurred.
  • at transformEvent (base transformation: line 4): Line at which library is referenced by the base transformation.
  • event['sub'] = sub(1,2): Line where lib function is called.

Questions? We're here to help.

Join the RudderStack Slack community or email us for support

Slack Join now → Email Reach out →