Linda

Linda's assignment for one of my oDesk interviews.

Raison d'etre

My name is Paulo Scardine and I live at Sao Paulo, Brazil. A few months ago I decided I don't want to have 10 million neighbours anymore, so I'm pursuing the "digital nomad" errand in order to move to a small town. So far I'm doing great at oDesk.

Linda Lo is a recruiter from oDesk (is she aware that her name means "pretty" in Portuguese?).

As part of a recruitment proccess I got the following assignment:

This should take you less than 20 minutes to reply.

Please provide a code sample in Python showing a moderately complicated operation in the context of a consumer app. It can be the RESTful interface, some data manipulation in response to user input, or processing and output based on the user’s data. Whichever it is, please provide a sample of of a few hundred lines of code from one of your projects.

This one is tough... Most of the code I write is covered by some NDA, is smaller than a few hundred lines or is obsolete by now. I had patches accepted for projects that have a high bar for contributors, like Django, Angular and Python - so I can code cleanly, write tests and documentation when required.

Write a small program that I could install on my AWS server that is a generator that gives the firstname of subscribers from a MySQL table, with user_id #s between 1234 and 1334, and that produces the name in English alphabetical order. The structure of the MySQL table can be anything you suggest.

I hope this serves as an answer for number 1 and 2; it is not a few hundred lines of code but Python being as concise as it is, a few hundred lines of Python are more in the 20 hours range than 20 minutes.

How many ways can you append or concatenate strings? Which of these ways is fastest? Easiest to read? Does your answer change based on count of strings? Or size of strings?

There are two idiomatic ways to concatenate strings.

# A
"a" + "b"
# B
"".(["a", "b"])

Short answer is... does it matter? Premature optimization is the root of all evil. That said, A is pretty ok for small strings and B performs better for a big number of strings.

Long answer is: performance can vary both in speed and memory consumption based on implementation, size of strings, number of strings, if they are bytecode or unicode and so on. Always profile.

Instructions

This works for any database supported by SQLAlchemy, not only for MySQL (you may have to install other database drivers). I assume you have the development libraries for MySQL client (on ubuntu, sudo apt-get install libmysqlclient-dev).

Clone the repo:

git clone https://github.com/scardine/linda
cd linda

Install requirements (creating a virtualenv before may be a good idea).

pip install -r requirements.txt

List commands:

$ fab -l

Available commands:

arguments  List arguments and defaults
drop       Drop table
getrange   Get a range of users based on user_id, default between 1234 and 1334
result     Get first name from a range based on user_id
setup      Creates table if it does not exist, and create 2000 fake users.

Get the list of arguments:

$ fab arguments

Arguments and defaults are:

    driver:   'mysql'
    username: 'root'
    password: ''
    dbhost:   'localhost'
    port:     '3307'
    database: 'test'
    table:    'users'

Usage:

    fab command:arg1=value1,arg2=value2,argN=valueN

I assume your users table has a field called user_id. If you don't have such a table yet, run the setup command in order to create the table and some fake users:

$ fab setup:driver=mysql,username=paulos,password=test,howmany=1500

Created user 1: Aldin Sutija
Created user 2: David Jaijeet
Created user 3: Conroy Clarise
Created user 4: Aldrich Neyer
Created user 5: Ransell Hella
...

And finally the assignment:

$ fab getrange:driver=mysql,username=paulos,password=test,start=1234,end=1244

Connecting to mysql://paulos:test@db/test
1234    Ulises Kuo-Chuan
1235    Waverley Shing
1236    Hollis Haibo
1237    Courtney Tijeun
1238    Stephan Merritt
1239    Ring Arno
1240    Peter Huichaun
1241    Roberto Moni
1242    Vincent Thersa
1243    Dare Daesik
1244    Jarret Ta

Done.

Only the first names, orderded:

$ fab result:driver=mysql,username=paulos,password=test,dbhost=db,port=3307,start=1234,end=1244

Connecting to mysql://paulos:test@db/test
Courtney
Dare
Hollis
Jarret
Peter
Ring
Roberto
Stephan
Ulises
Vincent
Waverley

Done.