Flask First-Timer

The year was 1994. I was a student at UIC. There was a buzz in the lab where I work. Mosaic had been out
for 6 months. Now there was a new version of BBEdit out that had support for HTML. I already wanted to
learn perl so I thought this would be a great opportunity to write a perl CGI program for the Daleks game.
1994

buzz

Mosaic

BBEdit

HTML

perl

daleks

If you don't know the Daleks game, it's a simple game where you're on a grid you avoid the killer robots by making them
run into each other. You make a move, and then the computers make a move. It's a great game with which to learn a
new language or new environment. Since I didn't know how to save data on the server I passed the entire board as the
part of the query string.

http://www.isaacsukin.com/news/2012/01/daleks-robot-puzzle-game

sessions

http://example.com/cgi-bin/robots.pl?board=..R..X..RR.R

Since I didn't understand forms yet, all commands were
simple anchor tags:
<a href="/cgi-bin/robots.pl?board=.R.X..&command=left">Move Left</a>
<a href="/cgi-bin/robots.pl?board=.R.X..&command=right">Move Right</a>
<a href="/cgi-bin/robots.pl?board=.R.X..&command=NewGame">New Game</a>

The program worked great, and we enjoyed playing it. I learned perl and HTML and CGI programming at the same time. I also
learned that it caused someone else's server to run out of disk space. Another student decided he wanted to learn how to
write a web crawler. He'd search for links on a page, log each one to a file, and then follow them. His crawler found my robots
program, and got addicted. Happily playing game after game and logging each move until it ran out of disk space. Oops!

learned

disk space

crawler

Hello. My name is Aijaz, and I've been breaking things on the web since 1994. This is a
story about how I wound up where I am today, with Flask, and what I learned along the
way.
Oops!

way.
/index.html
Hello

way.
@_aijaz_

I started my professional career in 1995 as a call processing developer at Motorola. If you used a cell phone in the late 1990s, chances are you were
running my code. After about 5 years, I quit and started my own Web Hosting and Application Development company. When it became obvious that
that wasn't sustainable, I moved to the financial industry and started working at Citadel, in this very building. 8 years later, I decided to switch careers
and become an iOS developer. I'm currently working for FastModel Sports where I write iOS apps for NBA and NCAA basketball coaches. But today I
want to talk to about the web.
/about/

I started my professional career in 1995 as a call processing developer at Motorola. If you used a cell phone in the late 1990s, chances are you were
running my code. After about 5 years, I quit and started my own Web Hosting and Application Development company. When it became obvious
that that wasn't sustainable, I moved to the financial industry and started working at Citadel, in this very building. 8 years later, I decided to switch
careers and become an iOS developer. I'm currently working for FastModel Sports where I write iOS apps for NBA and NCAA basketball coaches. But
today I want to talk to about the web.

You already know about robots.pl. Perl, CGI. using cgi-lib.pl
1994

I was asked to make a website - we called them homepages back then - for a Muslim
organization. That was the first time I became a webmaster. This was the website in all its
mid 1990s glory.
1995

- Gratuitous Landing page CHECK
- Drop shadow? CHECK
- Emboss and beveled text? CHECK
- Arbitrary perspective? CHECK
- HTML image maps? CHECK
- Custom horizontal rules? CHECK
- Text rendered as an image because the
browsers couldn't handle the formatting? CHECK
- The only thing it's missing is a lovingly

At that time it was not possible to display Arabic text in the browser, but I had a ton of text that needed to be displayed. I could scan the text from print,
but I didn't have too much disk space on my hosted account. So I went to Boutell.com, downloaded his gd C library. Then I modified it so it could
convert ascii text to scanned bitmaps, and joined those bitmaps to create gifs on the fly. Right to left, proportional widths. This way, a large image like
this, instead of taking 100K would only be 400 bytes. Of all the things I've ever done on the web, this is the one I'm most proud of. Because it was
new.
arabic

new.
scan

new.
disk space

new.
Boutell.com

new.
gd

new.
scanned chars

At that time it was not possible to display Arabic text in the browser, but I had a ton of text that needed to be displayed. I could scan the text
from print, but I didn't have too much disk space on my hosted account. So I went to Boutell.com, downloaded his gd C library. Then I modified
it so it could convert ascii text to scanned bitmaps, and joined those bitmaps to create gifs on the fly. This way, a large image like this, instead
of taking 100K would only be 400 bytes. Of all the things I've ever done on the web, this is the one I'm most proud of. Because it was new.
a.out
void main(int argc, char ** argv)
{
gdImagePtr im, im2;
FILE *out;
//...
printf("Content-type: image/gifnn");
/* Allocate the image: with a horiz padding */
im = gdImageCreate(MAXWIDTH + 10, height * 52);
// ...
/* Output the image to stdout. */
gdImageInterlace(im, 1);
gdImageGif(im, stdout);
/* Destroy the image in memory. */
gdImageDestroy(im);
}

it so it could convert ascii text to scanned bitmaps, and joined those bitmaps to create gifs on the fly. This way, a large image like this, instead of
taking 100K would only be 400 bytes. Of all the things I've ever done on the web, this is the one I'm most proud of. Because it was new.
tiny

it so it could convert ascii text to scanned bitmaps, and joined those bitmaps to create gifs on the fly. This way, a large image like this, instead
of taking 100K would only be 400 bytes. Of all the things I've ever done on the web, this is the one I'm most proud of. Because it was new.
proud

I got a chance to take a "Webmastering" class. Even though the title was cheesy, this was one of the best classes I
ever took. They spent an entire day talking about how Apache Modules worked and how they were written with the
HTTP specification in mind. Even though I really didn't want to write Apache Modules in C, I finally really understood
how the different components worked together.
1998

webmastering

apache modules

And when Modperl came along, I was able to create complex websites that were more
than single form-based pages. The first app I created was absolutely horrid. It was an e-
commerce app, and when I look at it now, I can see it was UGLY.
2000

mod_perl

e-commerce

UGLY

But, I kept reading and learning and with each eCommerce app or CRM website, I got better. Learned new things.
Became better at SQL. As time passed I started getting a nagging feeling - I was becoming too comfortable with my
stack. I started ignoring new things out there like the popular templating toolkits because I had written my own back in
the 90s. I started to feel that the world was passing me by, but I was too busy to adapt.
reading

comfortable

busy

Once I started working at Citadel upstairs my webdev activity came almost to a standstill. I had switched over
to the financial industry. I was mantaining existing apps here and there, but not really doing too much new stuff.
It was only in 2009 when I started doing some internal web apps. Again, using Mod_perl, apache httpd 1.3
2005

Citadel

standstill

internal apps

The turning point was in 2012. My sister-in-law was getting married. She wanted a simple website. A pretty one-page thing that would give guests venue and
accomodation information, and would allow them to RSVP. We've all done this dozens of times, right? I fired up a Linux virtual server, installed Apache httpd 2, perl. And
then everything failed. Modperl didn't install. I don't wanna bore you with the details, but for that one simple website I spent an entire **weekend** setting up the server and
then writing a blog post about it because in 2012 you could not find **instructions** on how to set up modperl using current versions of perl or apache. Perl was stagnating,
and the formerly vibrant community had long ago moved to greener pastures (like python). That's when I knew: my next website would have to be written in python.
turning point

one page

failed

weekend

no instructions

stagnating

greener pastures

(python)

I will now take a 15 second break and play a relevant video
clip
INTERMISSION

Fast forward to last November. My brother was starting an Indian delivery-only restaurant preparation and delivery
service and he needed a website as well as a back-end service for the inevitable mobile app. This was my chance to
start from scratch, and not be burdened by the 'old way of doing things.' This was my chance to get out of my comfort
zone and use the language that had been tempting me for the last decade: python.
TurboTiffin

Fast forward to last November. My brother was starting an Indian food preparation and delivery service and he needed a
website as well as a back-end service for the inevitable mobile app. This was my chance to start from scratch, and not
be burdened by the 'old way of doing things.' This was my chance to get out of my comfort zone and use the language
that had been tempting me for the last decade: python.
restaurant

Fast forward to last November. My brother was starting an Indian food preparation and delivery service and he needed a
website as well as a back-end service for the inevitable mobile app. This was my chance to start from scratch, and not
be burdened by the 'old way of doing things.' This was my chance to get out of my comfort zone and use the language
that had been tempting me for the last decade: python.
start from scratch

I knew about Django, and had tried to pick it up several times over the years, but there was something about it that I
just didn't like. I still don't know what it is. People say it's monolithic. Maybe. Maybe the problems that the Django
developers were solving didn't seem like the problems I wanted to solve. So the breakthrough came like so many other
breakthroughs in my life. I went to Google and typed in: Django vs...
django

I knew about Django, and had tried to pick it up several times over the years, but there was something about it that I
just didn't like. I still don't know what it is. People say it's monolithic. Maybe. Maybe the problems that the Django
developers were solving didn't seem like the problems I wanted to solve. So the breakthrough came like so many other
breakthroughs in my life. I went to Google and typed in: Django vs...
meh

Huh! Flask. Wonder what that's all about. I found
Miguel Grinberg's excellent series of posts on
Flask, bought his book, and that's when I realized
that this was the framework for me. I LOVED the fact
that the Flask book was thin. I LOVED the fact that I
was getting excited about the whole rigamarole:
- Create a virtual environment
- pip3 install all the things
- Run it locally easily
- Install just the modules you want.
huh

that this was the framework for me. I LOVED the fact
that the Flask book was thin. I LOVED the fact that I
was getting excited about the whole rigamarole:
Miguel Grinberg

that this was the framework for me. I LOVED the
fact that the Flask book was thin. I LOVED the fact
that I was getting excited about the whole
rigamarole:
!

My requirements for the website and app were pretty ordinary. Now I'm gonna talk about 2 of them and my rationale for choosing
the solutions I did. This is the part where I ask you a favor. As I describe my solutions, please put your skeptics' hats on and try
to find flaws in my arguments or assumptions. If you think I've made the wrong decision, please tell me so. Either during the
presentation, or afterwards. Challenge everything I say. You'll be doing me a great service. Alright back to the requirements.
requirements

do me a solid

challenge!

This is the subsystem that I agonized over the most. The fundamental decision is: Should
I use the high-level ORM that is Flask-SQLAlchemy or should I use raw SQL? I tried to
enumerate the pros and cons of using SQLAchemy
database

This is the subsystem that I agonized over the most. The fundamental decision is: Should
I use the high-level ORM that is Flask-SQLAlchemy or should I use raw SQL? I tried to
enumerate the pros and cons of using SQLAchemy
SQLAlchemy?

- db independence
- easy integration
- focus on models
- connection pooling
pros
» ease of use

easy integration
- focus on models
pros
» ease of use
» db independence

focus on models
pros
» ease of use
» db independence
» easy integration

pros
» ease of use
» db independence
» easy integration
» focus on models

pros
» ease of use
» db independence
» easy integration
» focus on models
» connection pooling

I didn't want to have to master yet another new
thing just to get version 1.0 working well. I
expected to spend a lot of time working with
Flask, and retraining myself to think like a
Python developer.
- comfort w/ SQL
- PostgreSQL 4 evah
- mobilecontext shifts
- multiple clients
cons
» time

I am really comfortable with SQL. After
working for 8 years with one of the best DBAs
in the country upstairs, it's easy for me to
think in terms of multi-table joins.
- PostgreSQL 4 evah
- multiple clients
- undo
cons
» time
» comfort w/ SQL

I liked the fact my code would work just as well
with PostgreSQL, sqlite3 or any other database.
But the truth is that I will always be using
PostgreSQL, even on my local mac.
- multiple clients
- undo
cons
» time
» comfort w/ SQL
» PostgreSQL 4 evah

The mobile client would have its own sqlite3 relational
database. It would be similar to the one on the server, so
I would have fewer context shifts when moving from
backend development to mobile and back again.
- multiple clients
- undo
cons
» time
» comfort w/ SQL
» mobilecontext shifts

The Flask website would not be the only client of the database. I would have batch
jobs that run at different times of the day that update menus, charge customers'
cards for orders placed in advance and print deliver manifests and receipts. Of
course, I could use SQLAlchemy for those jobs as well, but then I'm reminded of the
final point?
- undo
cons
» time
» comfort w/ SQL
» multiple clients

What if I'm joining the Flask bandwagon too late? What if Flask is about to begin its
stagnation? Or, what if I realize it really isn't well suited for what I'm trying to do? How
much work will be required to undo this decision to move to Flask?
cons
» time
» comfort w/ SQL
» multiple clients
» undo

When I looked at all these things together I decide to go with the pure SQL route and on
top of that do something I had never done before. I put all the business logic in the
database. Stored procedures. Lots of them.
cons
» time
» comfort w/ SQL
» multiple clients
» undo

When I looked at all these things together I decide to go with the pure SQL route and on
top of that do something I had never done before. I put all the business logic in the
database. Stored procedures. Lots of them.
sql

Everything from logging in, to finding the price of a dish, figuring out the tax, placing an order, applying coupon codes,
EVERTHING would be in the database layer, written in PL/PGSQL. The client code, the Flask Python code, would
never perform a join on two tables. It would instead call stored procedures that would do all of the heavy lifting.
stored procedures

EVERTHING would be in the database layer, written in PL/PGSQL. The client code, the Flask Python code, would
never perform a join on two tables. It would instead call stored procedures that would do all of the heavy lifting.
pl/pgsql

EVERTHING would be in the database layer, written in PL/PGSQL. The client code, the Flask Python code, would never
perform a join on two tables. It would instead call stored procedures that would do all of the heavy lifting. So instead of
calling a bunch of code to create an order, I can just do this.
heavy lifting

So instead of calling a bunch of code to create an order, I can just do this. What this gives me is all my
business logic in one place. It's easy to write test cases and verify them. The regression tests themselves are
written as sql statement. It's easy to notice when tests fail. It's just another form of dependency injection
cur.execute("SELECT * FROM f_add_order (%s, %s, %s, %s)",
( session['person_id']
, epoch_date
, section
, items_list))

It also allows me to use the psql database prompt to run stored procedures that aren't yet
accessible from the admin web site. Every once in a while, for example, someone will
cancel an order. All I have to do is:
dependency injection

All the tables stay in a consistent state while the order is cancelled. I was a little afraid of
not getting connection pooling down right, but after some research I realized I could
create the connection pool when I initialize the app:
select f_mark_order_cancelled(3055);

def create_app(config_name) :
app = Flask(__name__)
app.config.from_object(config[config_name])
config[config_name].init_app(app)
# attach routes and error pages here
from .main import main as main_blueprint
app.register_blueprint(main_blueprint)
# ...
app.connection_pool = ThreadedConnectionPool(min_conn, max_conn,
host=db_host, database=db_database_name, user=db_user_name)
return app

This is really for the REST services part of the app, as opposed to the website, where I used cookies. I know what I didn't
want: I didn't wanna use OAuth. It seemed icky for a restaurant to ask for your Google or Facebook credentials, for
example. You and I both know that I wouldn't actually get the credentials, but a very common reaction from users is: Oh,
I need to login via facebook to order a chicken tikka masala? Thanks, but no thanks. GrubHub it is.
authentication

It seemed icky for a restaurant to ask for your Google or Facebook credentials, for example. You and I both know that I wouldn't actually get the
credentials, but a very common reaction from users is: Oh, I need to login via facebook to order a chicken tikka masala? Thanks, but no thanks.
GrubHub it is. The other reason I decided not to use OAuth is that I really need the users' email addresses. This is how I send them receipts, let them
know when their credit cards have expired and communicate with them in general. I wanted to make sure that the email addresses I have on file are the
same adresses with which the users wish to communicate with TurboTiffin.
no OAuth

The other reason I decided not to use OAuth is that I really need the users' email addresses. This is how I send them receipts, let them know when
their credit cards have expired and communicate with them in general. I wanted to make sure that the email addresses I have on file are the same
adresses with which the users wish to communicate with TurboTiffin. Once the user authenticates with their email and password I create an token that
they can use in lieu of sending me their password every time. This token expires after a few minutes, so that the window of opportunity of using a
stolen token is relatively small.
emails

Once the user authenticates with their email and password I create an token that they can use in lieu of sending me their password
every time. This token expires after a few minutes, so that the window of opportunity of using a stolen token is relatively small. Now,
what Grinberg suggests is to use the itsdangerous package. Take the user id and expiration date and cryptographically sign these
two and return the result as a token. The beauty of this system is that the web server doesn't need to store the token locally. The token
has all the information the server needs, in a tamper-proof format.
token

Now, what Grinberg suggests is to use the itsdangerous package. Take the user id and expiration date and cryptographically sign these two and return the
result as a token. The beauty of this system is that the web server doesn't need to store the token locally. The token has all the information the server needs, in a
tamper-proof format. I decided not to go that route. I generate a random token and store it the database in clear text. I considered the risks of storing the token
in clear text, and for this application, if you had access to the token, you either had access to the mobile client's secure storage, where the user id and password
are also stored, or you have access to the server database. In either case, knowing the token does not increase the severity of the breach, and unlike storing the
password in cleartext, knowing the token doesn't give you access to other accounts owned by the same person.
itsdangerous

I decided not to go that route. I generate a random token and store it the database in clear text. I considered the risks of storing the token in clear
text, and for this application, if you had access to the token, you either had access to the mobile client's secure storage, where the user id and
password are also stored, or you have access to the server database. In either case, knowing the token does not increase the severity of the
breach, and unlike storing the password in cleartext, knowing the token doesn't give you access to other accounts owned by the same person.
tamper-proof

I generate a random token and store it the database in clear text. I considered the risks of storing the token in clear text, and for this
application, if you had access to the token, you either had access to the mobile client's secure storage, where the user id and password
are also stored, or you have access to the server database. In either case, knowing the token does not increase the severity of the breach,
and unlike storing the password in cleartext, knowing the token doesn't give you access to other accounts owned by the same person.
random

cleartext

mobile

server

In either case, knowing the token does not increase the severity of the breach, and unlike storing the password in cleartext, knowing the token doesn't give you access to other
accounts owned by the same person. I was concerned about the impact of adding a database lookup for every page request, but it appears that the speed is still pretty good: I'm
getting around 20ms to serve a page. So that's pretty good, right? The other effect of having the token stored in the database is that you can quickly see how many people have
been active on your website during the amount of time equal to your token lifespan. And, by deleting a token, you can easily block out clients that may be hitting your server too
frequently. Not that I need to worry about this on a small website, but these are the rationalizations that I came up with. I will be very interested to hear your comments on this.
severity

I was concerned about the impact of adding a database lookup for every page request, but it appears that the speed is still pretty good: I'm getting
around 20ms to serve a page. So that's pretty good, right? The other effect of having the token stored in the database is that you can quickly see how
many people have been active on your website during the amount of time equal to your token lifespan. And, by deleting a token, you can easily block
out clients that may be hitting your server too frequently. Not that I need to worry about this on a small website, but these are the rationalizations that I
came up with. I will be very interested to hear your comments on this.
impact on speed

GET /admin/receipts => generated 1291 bytes in 21 msecs

active

block out

So there we have it. This is the story of how I got from a perl cgi robots game in 1994
to delivering people Indian food using Flask today. What did I learn along the way?
comments

Try to understand how things work under
the hood
NEXT: SHARE WHAT YOU LEARN
» deep learning

Write blog posts. Even if no one reads them, you'll
organize your thoughts. Or give talks. Like this one
NEXT: KNOW WHEN TO STOP
» deep learning
» share what you learn

Don't stick blindly to one technology or
framework. Know when to move on.
NEXT: FAILURE IS CHARACTER BUILDER
» deep learning
» know when to stop

When you go down a certain path and give up because it doesn't suit
your purpose, don't think of them as bad experiences, think of them as
learning experiences and character builders
NEXT: SECOND-MOST IMPORTANT TASK IS TO WRITE BEAUTIFUL
CODE
» deep learning
» character builders

Your second-most important task is to create beautiful
code. Your most important task is to ship working code.
FINALLY: CHANGE YOUR OPINION
» deep learning
» ship on time

Be ready to change your opinion when faced with new
data. It's called being an adult.
» deep learning
» ship on time
» change opinion

Aijaz Ansari
@_aijaz_
http://aijaz.net

Flask First-Timer

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