Shantanu's Blog

Database Consultant

January 30, 2015

 

Using string templates in python

$to and $from in the docstring can be used as a template so that the values from dictionary can replace the placeholder using substitute method of string.template object. neat !

import string
tmpl = string.Template('''
Hi ${to},
welcome to the club
Regards,
$from
''')
dct={'to': 'Rick', 'from':'Stuart'}

tmpl.substitute(dct)

Labels:


 

lambda functions in python

def lambda_adder(a, b):
    return a+b

This function can also be written as lambda function as shown below:

lambda_adder = lambda a,b: a+b

Call either of the functions above using:
lambda_adder(1,2)

Labels:


January 29, 2015

 

email notification of S3 activity

There is an easy way to get alerts of all your S3 account activity.

1) Go to SNS home page here:
https://console.aws.amazon.com/sns/home?region=us-east-1

2) Create new topic
Topic name can be something like "s3_to_email"

3) Note the Topic ARN:
arn:aws:sns:us-east-1:94331768506:s3_to_email

4) View/Edit Topic policy: Advance view

5) Add the following code after changing the ARN

  {
   "Sid": "zzz",
   "Effect": "Allow",
   "Principal": {
    "AWS": "*"
   },
   "Action": "SNS:Publish",
   "Resource": "arn:aws:sns:us-east-1:94331768516:test",
   "Condition": {
    "ArnLike": {
     "aws:SourceArn": "arn:aws:s3:*:*"
    }
   }
  }

6) Click on "Create Subscription" and subscribe to the topic using email protocol. You will have to check your email and confirm your subscription.

That's it. Now select a bucket in S3 - Choose Events from Properties And add an event pointing to SNS topic that you have just created.

This will start sending you email as and when a file is added to that bucket.
This event needs to be applied to all buckets. A task that can be accomplished by boto.
_____

Another way is to add a rule to cloudwatch.

https://console.aws.amazon.com/cloudwatch/home?region=us-east-1#rules:action=create

choose "Rules" from Events.
Service Name "EC2" in Event Pattern.

Choose a lambda function as target that will simply email the contents.

Labels: , ,


January 26, 2015

 

Memory usage report

Here is an utility to accurately report the memory usage for a program.

https://github.com/pixelb/ps_mem

ps_mem [-h|--help] [-p PID,...] [-s|--split-args] [-t|--total] [-w N]
Example output:

 Private  +   Shared  =  RAM used       Program

 34.6 MiB +   1.0 MiB =  35.7 MiB       gnome-terminal
139.8 MiB +   2.3 MiB = 142.1 MiB       firefox
291.8 MiB +   2.5 MiB = 294.3 MiB       gnome-shell
272.2 MiB +  43.9 MiB = 316.1 MiB       chrome (12)
913.9 MiB +   3.2 MiB = 917.1 MiB       thunderbird
---------------------------------
                          1.9 GiB
=================================

Labels: ,


January 25, 2015

 

comparing numbers in python

set comparison as shown below is faster than the for-loop comparison in python.

a = set(range(7045000000,7045099999))
myset=[]
with open('Output21.txt3' , 'r') as f:
    for line in f:
        myl = line[:5]
        if myl == '70450':
            myset.append(int(line.strip('\n')))
b=set(myset)      
a-b
_____

myl=[]
with open("Output21.txt3") as f:
    rd=f.readlines()
    x=[t.strip("\n") for t in rd if t[:5] == '70450']
    for i in range(7045000000,7045099999):
        if str(i) not in x:
            myl.append(i)


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January 24, 2015

 

query text files

Usually we need to import the CSV data to SQL in order to run the queries. How about running queries directly on the text file?

# git clone https://github.com/harelba/q.git

# cd q

# chmod +x ./bin/q

# ./bin/q "SELECT COUNT(1) FROM examples/exampledatafile"
248

If git is not installed, use the single file found here...

# wget -O q https://cdn.rawgit.com/harelba/q/1.5.0/bin/q?source=install_page&table=1

Interesting!

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