Python 2.7 to python 3.7 Print error in code

Python
1

this python 2.7 print code has to be converted to Python 3.7 code

print "Found %d instances that need backing up" % len(instances) 
print "Retaining snapshot %s of volume %s from instance %s for %d days" % (
                snap['SnapshotId'],
                vol_id,
                instance['InstanceId'],
                retention_days,
            )

this code is giving error

print("Found %d instances that need backing up" % len(instances))
print("Retaining snapshot %s of volume %s from instance %s for %d days" % (
                snap['SnapshotId'],
                vol_id,
                instance['InstanceId'],
                retention_days,
            ))

Please let me know how we can convert this print to python 3.7

2

First install 2to3 module pip install 2to3. Then in the console type 2to3 yourfile name.py -w
You can use some flags for more customization:

  • the -w flag to enable writeback
  • the -n to disable backups
1 Like
3

Hi Naib, I used the 2to3 module.
But still, I get errors on Print on Python 3.7 on AWS Lambda.

I get below full errors.

{
“errorMessage”: “Syntax error in module ‘lambda_function’: invalid syntax (lambda_function.py, line 22)”,
“errorType”: “Runtime.UserCodeSyntaxError”,
“stackTrace”: [
" File “/var/task/lambda_function.py” Line 22\n print “Found %d instances that need backing up” % len(instances)\n"
]
}

Function Logs
START RequestId: 8a2824a5-edd9-4243-b54a-d40782325f2f Version: $LATEST
[ERROR] Runtime.UserCodeSyntaxError: Syntax error in module ‘lambda_function’: invalid syntax (lambda_function.py, line 22)
Traceback (most recent call last):
File “/var/task/lambda_function.py” Line 22
print “Found %d instances that need backing up” % len(instances)
END RequestId: 8a2824a5-edd9-4243-b54a-d40782325f2f
REPORT RequestId: 8a2824a5-edd9-4243-b54a-d40782325f2f Duration: 21.14 ms Billed Duration: 22 ms Memory Size: 128 MB Max Memory Used: 48 MB Init Duration: 122.09 ms

Request ID
8a2824a5-edd9-4243-b54a-d40782325f2f

4

Hi Naib, this is the full python 2.7 script, that has to be run in AWS Lambda python 3.7

import boto3
import collections
import datetime

ec = boto3.client('ec2')

def lambda_handler(event, context):
    reservations = ec.describe_instances(
        Filters=[
            {'Name': 'tag-key', 'Values': ['backup', 'Backup']},
        ]
    ).get(
        'Reservations', []
    )

    instances = sum(
        [
            [i for i in r['Instances']]
            for r in reservations
        ], [])

    print "Found %d instances that need backing up" % len(instances)

    to_tag = collections.defaultdict(list)

    for instance in instances:
        try:
            retention_days = [
                int(t.get('Value')) for t in instance['Tags']
                if t['Key'] == 'Retention'][0]
        except IndexError:
            retention_days = 7

        for dev in instance['BlockDeviceMappings']:
            if dev.get('Ebs', None) is None:
                continue
            vol_id = dev['Ebs']['VolumeId']
            print "Found EBS volume %s on instance %s" % (
                vol_id, instance['InstanceId'])

            snap = ec.create_snapshot(
                VolumeId=vol_id,
            )

            to_tag[retention_days].append(snap['SnapshotId'])

            print "Retaining snapshot %s of volume %s from instance %s for %d days" % (
                snap['SnapshotId'],
                vol_id,
                instance['InstanceId'],
                retention_days,
            )


    for retention_days in to_tag.keys():
        delete_date = datetime.date.today() + datetime.timedelta(days=retention_days)
        delete_fmt = delete_date.strftime('%Y-%m-%d')
        print "Will delete %d snapshots on %s" % (len(to_tag[retention_days]), delete_fmt)
        ec.create_tags(
            Resources=to_tag[retention_days],
            Tags=[
                {'Key': 'DeleteOn', 'Value': delete_fmt},
            ]
        )
5 
print(f"Found {len(instances)} that need backing up") #notice the f before the string
print(f"Retaining snapshot {snap['SnapshotId']} of volume {vol_id} from instance {instance['InstanceId']} for {retention_days} days")

the expression between curly braces will be evaluated and transformed to str.

you can also use string method format for better organization of code.

print("Found {num_of_instances} instances that need backing up".format(num_of_instances=len(instances)))

Search for python3 string formatting, the way you did it with % is the old way and is less emphasized nowadays.

6

Thanks Nzz,

It got resolved. I had click on Deploy button on AWS Lambda, and then run it.

Thanks everyone for help…

7 
print("Found {} instances that need backing up".format(len(instances)))

Even this can work , the content inside curly braces is just a place holder to extract values orderly from format()

8

Thanks Sargun… I clicked on Deploy, and it started working

9

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