Why I Hate Django
Cal Henderson

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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Wordpress
Yahoo
Mediawiki Facebook
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Wordpress
Yahoo
Delicious
Digg
Mediawiki Facebook
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Flamework
Serious Toolset
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Flamework Flink
Flint Flotos
Flinderbox Flictionary
Flaux Flops
Flag 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
Python
Frameworks
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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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DjangoCore
The Album
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Also, a wizard
Simon “Stinky” Willison
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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 Haskell
Or Erlang
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But not that trendy
It’s no ruby
Or Haskell
Or Erlang
Or Scala
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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
E
G
A
U
G
N
A
L
N
O
O
[M
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__import__()
from future import awesome
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Basically, for hippies
Scared of real
OO languages
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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:
easier
faster
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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Other
Data store
Services
Data Model
Business
Logic
Request Interaction
Templates
Dispatcher Logic
Framework
Users
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Great for getting started
Slows you down later?
What is it doing in there?
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Fast
Easy
Scalable
Flexible
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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
But they only apply
When being really silly
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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
{% endif %}
{if $edit_mode}
woo
{/if}
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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Unreadable SQL
SELECT
`app_userprofile`.`user_id`,`app_userprofile`.`account_status`,`app_userp
rofile`.`account_status_reason`,`app_userprofile`.`account_delete_type`,`
app_userprofile`.`syndication_key`,`app_userprofile`.`blurb`,`app_userpro
file`.`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_pho
to`,`app_userprofile`.`medium_photo`,`app_userprofile`.`large_photo`,`ap
p_userprofile`.`orig_photo`,`app_userprofile`.`bday_month`,`app_userpro
file`.`bday_day`,`app_userprofile`.`bday_year`,`app_userprofile`.`is_pro`,`a
pp_userprofile`.`privacy_settings_id`,`app_userprofile`.`email_settings_id
`,`app_userprofile`.`preference_settings_id`,`app_userprofile`.`ad_counte
r`,`app_userprofile`.`num_friends`,`app_userprofile`.`num_fans`,`app_user
profile`.`num_feeds`,`app_userprofile`.`num_blocked_fans`,`app_userpro
file`.`num_friend_requests`,`app_userprofile`.`default_set_id`,`app_userpr
ofile`.`invite_id`,`app_userprofile`.`invite_round`,`app_userprofile`.`avail_in
vites`,`app_userprofile`.`original_email` FROM `app_userprofile` WHERE
(`app_userprofile`.`user_id` = 1)
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Unreadable SQL
SELECT * FROM `app_userprofile` WHERE
`user_id` = 1
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SELECT * is fast!
Faster over the wire
Faster to parse
Easier to debug
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Unreadable SQL
SELECT
`app_note`.`id`,`app_note`.`type`,`app_note`.`body`,`app_note
`.`sender_id`,`app_note`.`date_sent`,`app_note`.`num_recipie
nts`,`app_note`.`recipient_type`,`app_note`.`set_id`,`app_not
e`.`direct_to_id`,`app_note`.`media_file_id`,`app_note`.`url`,`a
pp_note`.`url_inline`,`app_note`.`url_clicks`,`app_note`.`embe
d_id`,`app_note`.`event_id`,`app_note`.`is_direct`,`app_note`.`
is_public`,`app_note`.`is_deleted`,`app_note`.`is_ad`,`app_no
te`.`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
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Unreadable SQL
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
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Django makes me
scared of joins
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Actually,
JOINs are evil
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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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UPDATE foo SET x=x+1
Makes consistency hard!
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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
Tables are never
big enough
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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?
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thanks
(now go make it better)

Photo credits
flickr.com/photos/wilson/18685396/ flickr.com/photos/sharynmorrow/2571566304/
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flickr.com/photos/uhop/105063089/ flickr.com/photos/florathexplora/286035943/
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flickr.com/photos/plasticbag/91453376/ flickr.com/photos/webguru4god/2233500779/
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flickr.com/photos/zenoc/1408162618/ flickr.com/photos/emdot/195189924/
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flickr.com/photos/subinev/27810058/ flickr.com/photos/kayepants/391645870/
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flickr.com/photos/kaptainkobold/2531797176/ flickr.com/photos/ppowers/793939285/
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flickr.com/photos/esti/243781036/ flickr.com/photos/dinesh_valke/425540358/
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flickr.com/photos/oneras/253617128/ flickr.com/photos/hawkexpress/306276212/
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flickr.com/photos/josefstuefer/72512671/ flickr.com/photos/cedric1981/383614033/
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flickr.com/photos/pgoyette/168076182/ flickr.com/photos/macspite/1118042091/
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flickr.com/photos/paulhammond/2825869449/ flickr.com/photos/jpstanley/1440357613/
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flickr.com/photos/nez/378348754/ flickr.com/photos/ashclements/248887492/
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flickr.com/photos/calevans/2265863104/ flickr.com/photos/kecko/1876479840/
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flickr.com/photos/mbiddulph/416190643/ flickr.com/photos/difusa/131100622/
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flickr.com/photos/obliterated/2249663391/ flickr.com/photos/amagill/378984660/
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flickr.com/photos/salim/67753003/ flickr.com/photos/bea_k63w-wa/2466009108/
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flickr.com/photos/sosalem/2816909110/ flickr.com/photos/namullim/2096115820/
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flickr.com/photos/radiorover/324193883/ flickr.com/photos/lotterymonkey/175248733/
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flickr.com/photos/nickwheeleroz/2773776799/ flickr.com/photos/13519089@N03/1380483002/
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flickr.com/photos/rse/22972901/ flickr.com/photos/gswj/10344097/
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flickr.com/photos/rougerouge/534615363/ flickr.com/photos/deanj/67607256/
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flickr.com/photos/hawkexpress/386355092/ flickr.com/photos/malias/2218694639/
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flickr.com/photos/escalla/438817719/ flickr.com/photos/clintjcl/120760767/
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flickr.com/photos/mknightphoto/2295688304/ flickr.com/photos/grandpamikey/2228239585/
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flickr.com/photos/petereed/138369750/ flickr.com/photos/lea/2829752510/
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flickr.com/photos/superamit/196481424/
•
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More photo credits
flickr.com/photos/simon999/2419051858/ flickr.com/photos/jordanroher/228435564/
• •
flickr.com/photos/tonyjcase/2172060723/ flickr.com/photos/tambako/2524829095/
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flickr.com/photos/heypaul/1428681/ flickr.com/photos/66132721@N00/2725908636/
• •
flickr.com/photos/swisscan/2308034084/ flickr.com/photos/freeparking/1279927021/
• •
flickr.com/photos/apollonia666/310793656/ flickr.com/photos/drurydrama/1352506223/
• •
flickr.com/photos/bdorfman/15846725/ flickr.com/photos/mn_francis/397620193/
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flickr.com/photos/wishymom/566394520/ flickr.com/photos/dramaqueennorma/273371415/
• •
flickr.com/photos/jgarber/121886004/ flickr.com/photos/chasqui/2338990305/
• •
flickr.com/photos/eole/380316678/ flickr.com/photos/cityhunter12/2574288725/
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flickr.com/photos/917press/1940509163/ flickr.com/photos/akbuthod/1508537255/
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flickr.com/photos/wallyg/476718069/ flickr.com/photos/nunoforos/2811186142/
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flickr.com/photos/biwook/390088839/ flickr.com/photos/marcusjb/432600086/
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flickr.com/photos/bdjsb7/1674027307/ flickr.com/photos/12495774@N02/2405297371/
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flickr.com/photos/naveenroy/314965221/ flickr.com/photos/larimdame/572477975/
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flickr.com/photos/wyldkyss/2757474674/ flickr.com/photos/harryharris/1525946537/
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flickr.com/photos/orinrobertjohn/409812627/ flickr.com/photos/davemorris/91808851/
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flickr.com/photos/candiedwomanire/1651870/ flickr.com/photos/aplumb/121285138/
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flickr.com/photos/dalvenjah/408497650/ flickr.com/photos/peebot/825451566/
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flickr.com/photos/krikit/2657457178/ flickr.com/photos/reillyb/2216541900/
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flickr.com/photos/w5nyv/2370344/ flickr.com/photos/steffe/423086866/
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flickr.com/photos/jordanfischer/72510316/ flickr.com/photos/ciordia/255983919/
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flickr.com/photos/tedsblog/91531710/ flickr.com/photos/wwworks/2472230611/
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flickr.com/photos/celesterc/1069893367/ flickr.com/photos/pnoid00/1909096140/
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flickr.com/photos/spacematters/766372252/ flickr.com/photos/jurvetson/2229899/
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flickr.com/photos/esti/147733640/ flickr.com/photos/foxypar4/766801643/
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flickr.com/photos/rbp/2833593771/ flickr.com/photos/wizardhere/2413404079/
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these slides are online:
iamcal.com/talks
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