Python function in AWS Lambda

Question

I am needing to run the following function below on AWS Lambda:

def subset_sum(numbers, target, partial=[]):
    s = sum(partial)

# check if the partial sum is equals to target
if s == target:
    print("sum(%s)=%s" % (partial, target))
if s >= target:
    return  # if we reach the number why bother to continue

for i in range(len(numbers)):
    n = numbers[i]
    remaining = numbers[i + 1:]
    subset_sum(remaining, target, partial + [n])

if __name__ == "__main__":
    subset_sum([1,2,3], 5)

Yet this one comes along and I can’t fix it:

{
  "errorMessage": "'>=' not supported between instances of 'int' and 'LambdaContext'",
  "errorType": "TypeError",
  "stackTrace": [
    [
      "/var/task/lambda_function.py",
      7,
      "subset_sum",
      "if s >= target:"
    ]
  ]
}

The original function has more values that take a long time so I’m trying to run on Lambda. The function returns the combination of numbers that result in the sum of the defined value (in case 5)

On the computer using py subset_sum.py works normally and returns 2 and 3 (which combined is equal to 5).

UPDATING

I made the modification as Tom replies. Now reports another error.

def lambda_handler(event, context):

    s = sum(event['partial'])

    if s == 5:
        print("sum(%s)=%s" % (event['partial'], 5))
        exit()
    if s >= 5:
        return

    for i in range(len(event['numbers'])):
        n = event['numbers'][i]
        remaining = event['numbers'][i + 1:]
        dict = {'numbers' : remaining, 'partial' : event['partial'] + [n]}
        lambda_handler(dict)

if __name__ == "__main__":
    dict = {'numbers' : [1,2,3], 'partial' : []}
    lambda_handler(dict)

Output from the Lambda

{
  "errorMessage": "'partial'",
  "errorType": "KeyError",
  "stackTrace": [
    [
      "/var/task/lambda_function.py",
      5,
      "lambda_handler",
      "s = sum(event['partial'])"
    ]
  ]
}

Print(Event) output at the very beginning of Handler

START RequestId: f3a45f36-b1fc-11e7-8f6d-d5a3a428a4fd Version: $LATEST
{'key3': 'value3', 'key2': 'value2', 'key1': 'value1'}
'partial': KeyError
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 7, in lambda_handler
    s = sum(event['partial'])
KeyError: 'partial'
END RequestId: f3a45f36-b1fc-11e7-8f6d-d5a3a428a4fd

Answer 1

If you set the function subset_sum Like Handler of your Lambda Function, the parameters that are passed are different from your test subset_sum([1,2,3], 5).

Handler invoke takes the parameters:

• Event - Event responsible for running the Lambda Function (API Gateway, Cloudwatch, etc);
• context - Information of Runtime.

The error happens by comparing what you are doing between an int and a Lambdacontext object.

The parameters should be accessed through the event, ex:

def my_handler(event, context):
    partial = event['partial']
    target = event['target']

    print(partial)
    print(target)

Documentation: http://docs.aws.amazon.com/lambda/latest/dg/python-programming-model-handler-types.html

EDIT

---

To set the test event values through the console:

Lambda -> (Select your Lambda Function) -> Select a test Event -> Configure test Events