WTF: Oops, already in my list

 I found an interesting loop pattern, used at several places in our code. It goes like this: 

• I create an empty list
• I start a loop to fill it
• Inside my loop, I create an object and add it to my list
• Still in the loop, I need to modify the object I just added, so I retrieve it from the list

An example here:

templates = []

index = 0

json_templates = json.loads(templates_as_str)

for template_file in json_templates:

    templates.add(get_template(template_file))

    template = templates[index]

    # Do some stuff on my template

    index += 1

So yes, I could have created my template reference before storing it in the list. But it's too late! I need to use an index now...

Python: Over formatting

In the Python project I work on, some colleague likes to use the string's format method. Sometimes a bit too much for my taste. For instance, I can often see this kind of code:

my_string = "{}-{}".format(part1, part2)

Usually, I prefer to use an f-string:

my_string = f"{part1}-{part2}"

But it could be a matter of taste. However, in some cases, I would prefer to use another approach.

For instance, in the case of the print method, there is already an existing pattern. I see often this kind of code:

print("The value is {}".format(value))

I replace it usually with this code:

print("The value is", value)

A bit more annoying is the use of format inside logging. I often see this code:

logger.info("The value is {}".format(value))

In case of logging, the pattern is here for a reason. If logging level is set to WARNING for instance, you want to avoid the string formatting, which takes some processing time. The preferred pattern is the following:

logger.info("The value is %s", value)

Finally, there are the cases where the use of format is completely insane. Here is an example:

my_string = "{}".format(value)

Maybe my knowledge of Python is too limited, but value being already a string, is there any difference with this code:

my_string = value

AWS: Read Timeout when Invoking Lambda

 I have an AWS Lambda that invokes another Lambda synchronously. Nothing was wrong with it until recently, when the other Lambda started performing more tasks and taking more time. Suddenly, the caller Lambda started failing with this weird message:

ReadTimeoutError: Read timeout on endpoint URL: "https://lambda.eu-central-1.amazonaws.com/2015-03-31/functions/MyOtherLambda/invocations"

Looking at the logs of my other Lambda, I could see that it ran fine, although it was executed several times. After some research on the Internet, I found this article from AWS support that explains that when invoking a Lambda synchronously, there is a default timeout of 60 seconds, and 3 retries. This can be configured when creating the client.

In Python using boto3 for instance, you have to use the Config object:

import boto3

from botocore.config import Config

lambda_client = boto3.client("lambda", config=Config(read_timeout=600))

Now, my invoked lambda has 10 minutes to perform its tasks.