Why I Hate Django

Why I Hate DjangoCal Henderson

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O HAI

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My happy face

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2.8 billion photos

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2.8 billion photos

1 per 2.3 people on earth

9.2 per US resident

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35k photos/sec

>2m photos/min

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Many thousand pages/sec

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Scale nerd

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Serious Language

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Yahoo

FacebookMediawiki

Wordpress

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Yahoo

FacebookMediawiki

Wordpress

DiggDelicious

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Flamework

Serious Toolset

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Flamework

Flint

Flinderbox

Flaux

Flag

Flink

Flotos

Flictionary

Flops

Fleng

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Why hate Django?

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What does he even know

about Django?

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Pownce

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A fucking blogging engine

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Why all the hate?

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An attack on several fronts

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An attack on several fronts

The team

PythonFrameworks

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Django itself

Performance

Scalability

Maintainability

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The Team

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Frameworks

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Struts

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Craig McClanahan

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Exhibit A : Beard

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But Struts is for suits!

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The Hot Shit

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Rails = Badass

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Instead?

A boy band?

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DjangoCoreThe Album

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Simon “Stinky” Willison

Also, a wizard

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Python

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Trendy

Google!

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But not that trendy

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But not that trendy

It’s no ruby

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But not that trendy

It’s no ruby

Or Haskell

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But not that trendy

It’s no ruby

Or ErlangOr Haskell

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But not that trendy

It’s no ruby

Or ErlangOr Scala

Or Haskell

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Significant Whitespace

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Salmon

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Universe of marshy force. Field sense

shallows the hatchery saying Hello,. World!.

Hydro. Power spring sometimes; snowmelt

powers snowmelt always.

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No quantum

superpositions

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“-”.join(array)

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Restarting the server?

WTF!?

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WSGIReloadMechanism

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“I buy my eggs at the cheese shop”- Aaron Straup Cope

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“I buy my eggs at the cheese shop”- Aaron Straup Cope

[MOON L

ANGUAGE]

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__import__()

from future import awesome

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Basically, for hippies

OO languages

Scared of real

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Frameworks

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Flamework is a framework

But what does that mean?

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Make common tasks:

faster

easier

error-free

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Show a list of photos

Write an API method

Kill all humans

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Front-tier frameworks

Act as glue

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Data store

BusinessLogic

InteractionLogic

TemplatesRequest

Dispatcher

Users

OtherServices

Data Model

Framework

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Great for getting started

Slows you down later?

What is it doing in there?

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Fast

Flexible

Easy

Scalable

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Large scale

is often not a good goal

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Skyscrapers are special

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Regular houses

Don’t need 10 story foundations

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Just build!

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Everything here is possible!

We care about easy

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Large Scale

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No multiple DB clusters

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Manual partitioning

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No multiple hosts per DB

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Where do we read from?

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How about now?

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How about now ?

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Read/write consistency

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Read/write consistency

LAG!!1

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Good for non-writing users

(logged out)

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Non time-sensitive data

Feeds

Read-only APIs

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Cool kids use

master/master pairs

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Consistent read/write

1. Write to side A

2. Read from side B

3. Replication occurs

4. FAIL

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Consistent read/write

1. Write to side A

2. Read from side A

3. ???

4. PROFIT!!

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Then we can start to get fancy!

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Where do we read/write?

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Abstraction FTW

db_query($cluster_name, $sql)

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No sharding

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WTF is sharding?

All about books

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Dewey Decimal

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But it can’t do everything

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Makes some things

‘impossible’

No shard walking

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Django knows our models

It’s possible

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If we accept constraints

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No external sequences

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Auto-incs can be bad

master/master

shards

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No automatic denormalization

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Counters would be easy!

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And copied fields too

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High

Performance

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It’s slow!

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There are limits

When being really silly

But they only apply

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Sessions

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OMG UR ON CRAK

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Extra DB table

A read on every page

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Lightweight = better

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Signed cookies

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No parallelization

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Multiple cache-requests

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Multiple multi-keyed reads

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Slow HTTP requests while

we’re doing other stuff

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Creates dumb SQL

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foo.exclude(bar = true)

WHERE (NOT (bar = 1))

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foo.exclude(bar = true)

WHERE bar != 1

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foo.filter(bar = false)

WHERE bar = 0

Indexable!

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Maintainability

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Maintainability

Awesomeness

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Verbose template syntax

<h1>{{ foo.bar }}</h1>

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<h1>{{ foo.bar }}</h1>

<h1>{$foo.bar}</h1>

3 extra characters!

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<h1>{{ foo.bar }}</h1>

<h1>{$foo.bar|e}</h1>

Well almost…

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{if $edit_mode}woo

{/if}

{% if edit_mode %}woo

{% endif %}

9 extra!

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Verbose template syntax

makes people cry

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No query debugger

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>>> from django.db import connection

>>> connection.queries

[{'sql': 'SELECT

polls_polls.id,polls_polls.question,polls_

polls.pub_date FROM polls_polls', 'time':

'0.002'}]

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>>> from django.db import connection

>>> connection.queries

[{'sql': 'SELECT

polls_polls.id,polls_polls.question,polls_

polls.pub_date FROM polls_polls', 'time':

'0.002'}]

Not good enough!

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Better, but not amazing

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Page summary

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Make it clickable…

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EXPLAIN is AWESOME

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And/or show the data

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MySQL Query Profiler

Enough data to

choke a whale

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Not smug enough

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SELECT `app_userprofile`.`user_id`,`app_userprofile`.`account_status`,`app_userprofile`.`account_status_reason`,`app_userprofile`.`account_delete_type`,`app_userprofile`.`syndication_key`,`app_userprofile`.`blurb`,`app_userprofile`.`location`,`app_userprofile`.`country`,`app_userprofile`.`postal_code`,`app_userprofile`.`gender`,`app_userprofile`.`theme`,`app_userprofile`.`tiny_photo`,`app_userprofile`.`small_photo`,`app_userprofile`.`smedium_photo`,`app_userprofile`.`medium_photo`,`app_userprofile`.`large_photo`,`app_userprofile`.`orig_photo`,`app_userprofile`.`bday_month`,`app_userprofile`.`bday_day`,`app_userprofile`.`bday_year`,`app_userprofile`.`is_pro`,`app_userprofile`.`privacy_settings_id`,`app_userprofile`.`email_settings_id`,`app_userprofile`.`preference_settings_id`,`app_userprofile`.`ad_counter`,`app_userprofile`.`num_friends`,`app_userprofile`.`num_fans`,`app_userprofile`.`num_feeds`,`app_userprofile`.`num_blocked_fans`,`app_userprofile`.`num_friend_requests`,`app_userprofile`.`default_set_id`,`app_userprofile`.`invite_id`,`app_userprofile`.`invite_round`,`app_userprofile`.`avail_invites`,`app_userprofile`.`original_email` FROM `app_userprofile` WHERE (`app_userprofile`.`user_id` = 1)

Unreadable SQL

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SELECT * FROM `app_userprofile` WHERE `user_id` = 1

Unreadable SQL

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SELECT * is fast!

Faster over the wire

Faster to parse

Easier to debug

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SELECT `app_note`.`id`,`app_note`.`type`,`app_note`.`body`,`app_note`.`sender_id`,`app_note`.`date_sent`,`app_note`.`num_recipients`,`app_note`.`recipient_type`,`app_note`.`set_id`,`app_note`.`direct_to_id`,`app_note`.`media_file_id`,`app_note`.`url`,`app_note`.`url_inline`,`app_note`.`url_clicks`,`app_note`.`embed_id`,`app_note`.`event_id`,`app_note`.`is_direct`,`app_note`.`is_public`,`app_note`.`is_deleted`,`app_note`.`is_ad`,`app_note`.`reply_to_id`,`app_note`.`forwarded_from_id`,`app_note`.`original_note_id`,`app_note`.`stars`,`app_note`.`rsvp` FROM `app_note` LEFT OUTER JOIN `app_userprofile_notes` AS `m2m_app_note__recipients` ON `app_note`.`id` = `m2m_app_note__recipients`.`note_id` WHERE ((NOT (`app_note`.`is_deleted` = True)) AND `m2m_app_note__recipients`.`userprofile_id` = 17573) ORDER BY `app_note`.`date_sent` DESC LIMIT 16

Unreadable SQL

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SELECT

n.*

FROM

app_note AS n

LEFT OUTER JOIN app_userprofile_notes AS l

ON

n.id=l.note_id

WHERE

n.is_deleted = False AND l.userprofile_id=17573

ORDER BY

n.date_sent DESC

LIMIT 16

Unreadable SQL

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Django makes me

scared of joins

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JOINs are evil

Actually,

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Low version number

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Suspiciously small

Django: 105 klocs

Flamework: 260 klocs

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Suspiciously small

Very long lines?

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Can’t pluralize octopus

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Commit all fields at once

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Race conditions!

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Dirty flags

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Don’t make Malcolm cry

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No simple way to inc/dec

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Makes consistency hard!

UPDATE foo SET x=x+1

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Character encoding

Input validation?

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Character encoding

Input validation?

(Probably broken)

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No mascot!?!

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Echidna?

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MAGICAL POWERS

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No deployment system

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Extending models

big enough

Tables are never

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Model changes

manage.py reset appname

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django-evolution

dmigrations

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What’s django

done for you

lately?

thanks

(now go make it better)

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Photo credits• flickr.com/photos/wilson/18685396/• flickr.com/photos/uhop/105063089/• flickr.com/photos/plasticbag/91453376/• flickr.com/photos/zenoc/1408162618/• flickr.com/photos/subinev/27810058/• flickr.com/photos/kaptainkobold/2531797176/• flickr.com/photos/esti/243781036/• flickr.com/photos/oneras/253617128/• flickr.com/photos/josefstuefer/72512671/• flickr.com/photos/pgoyette/168076182/• flickr.com/photos/paulhammond/2825869449/• flickr.com/photos/nez/378348754/• flickr.com/photos/calevans/2265863104/• flickr.com/photos/mbiddulph/416190643/• flickr.com/photos/obliterated/2249663391/• flickr.com/photos/salim/67753003/• flickr.com/photos/sosalem/2816909110/• flickr.com/photos/radiorover/324193883/• flickr.com/photos/nickwheeleroz/2773776799/• flickr.com/photos/rse/22972901/• flickr.com/photos/rougerouge/534615363/• flickr.com/photos/hawkexpress/386355092/• flickr.com/photos/escalla/438817719/• flickr.com/photos/mknightphoto/2295688304/• flickr.com/photos/petereed/138369750/

• flickr.com/photos/sharynmorrow/2571566304/• flickr.com/photos/florathexplora/286035943/• flickr.com/photos/webguru4god/2233500779/• flickr.com/photos/emdot/195189924/• flickr.com/photos/kayepants/391645870/• flickr.com/photos/ppowers/793939285/• flickr.com/photos/dinesh_valke/425540358/• flickr.com/photos/hawkexpress/306276212/• flickr.com/photos/cedric1981/383614033/• flickr.com/photos/macspite/1118042091/• flickr.com/photos/jpstanley/1440357613/• flickr.com/photos/ashclements/248887492/• flickr.com/photos/kecko/1876479840/• flickr.com/photos/difusa/131100622/• flickr.com/photos/amagill/378984660/• flickr.com/photos/bea_k63w-wa/2466009108/• flickr.com/photos/namullim/2096115820/• flickr.com/photos/lotterymonkey/175248733/• flickr.com/photos/13519089@N03/1380483002/• flickr.com/photos/gswj/10344097/• flickr.com/photos/deanj/67607256/• flickr.com/photos/malias/2218694639/• flickr.com/photos/clintjcl/120760767/• flickr.com/photos/grandpamikey/2228239585/• flickr.com/photos/lea/2829752510/• flickr.com/photos/superamit/196481424/

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More photo credits• flickr.com/photos/simon999/2419051858/• flickr.com/photos/tonyjcase/2172060723/• flickr.com/photos/heypaul/1428681/• flickr.com/photos/swisscan/2308034084/• flickr.com/photos/apollonia666/310793656/• flickr.com/photos/bdorfman/15846725/• flickr.com/photos/wishymom/566394520/• flickr.com/photos/jgarber/121886004/• flickr.com/photos/eole/380316678/• flickr.com/photos/917press/1940509163/• flickr.com/photos/wallyg/476718069/• flickr.com/photos/biwook/390088839/• flickr.com/photos/bdjsb7/1674027307/• flickr.com/photos/naveenroy/314965221/• flickr.com/photos/wyldkyss/2757474674/• flickr.com/photos/orinrobertjohn/409812627/• flickr.com/photos/candiedwomanire/1651870/• flickr.com/photos/dalvenjah/408497650/• flickr.com/photos/krikit/2657457178/• flickr.com/photos/w5nyv/2370344/• flickr.com/photos/jordanfischer/72510316/• flickr.com/photos/tedsblog/91531710/• flickr.com/photos/celesterc/1069893367/• flickr.com/photos/spacematters/766372252/• flickr.com/photos/esti/147733640/• flickr.com/photos/rbp/2833593771/

• flickr.com/photos/jordanroher/228435564/• flickr.com/photos/tambako/2524829095/• flickr.com/photos/66132721@N00/2725908636/• flickr.com/photos/freeparking/1279927021/• flickr.com/photos/drurydrama/1352506223/• flickr.com/photos/mn_francis/397620193/• flickr.com/photos/dramaqueennorma/273371415/• flickr.com/photos/chasqui/2338990305/• flickr.com/photos/cityhunter12/2574288725/• flickr.com/photos/akbuthod/1508537255/• flickr.com/photos/nunoforos/2811186142/• flickr.com/photos/marcusjb/432600086/• flickr.com/photos/12495774@N02/2405297371/• flickr.com/photos/larimdame/572477975/• flickr.com/photos/harryharris/1525946537/• flickr.com/photos/davemorris/91808851/• flickr.com/photos/aplumb/121285138/• flickr.com/photos/peebot/825451566/• flickr.com/photos/reillyb/2216541900/• flickr.com/photos/steffe/423086866/• flickr.com/photos/ciordia/255983919/• flickr.com/photos/wwworks/2472230611/• flickr.com/photos/pnoid00/1909096140/• flickr.com/photos/jurvetson/2229899/• flickr.com/photos/foxypar4/766801643/• flickr.com/photos/wizardhere/2413404079/

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these slides are online:

iamcal.com/talks