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Tag Archives: python
randomly selecting objects from an array in O(1)
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this python snippet was a fun read:
http://code.activestate.com/recipes/576564-walkers-alias-method-for-random-objects-with-diffe/
(also here in ruby)
Intermission: using Twisted to serve Django via wsgi
and now, while on break from our ongoing tutorial (table of contents).
are you tired of starting django and twisted via two separate processes, possibly having them run in two different shells for debugging purposes? i know i am.
fortunately, django and twisted can inter-operate – Django supports the Python wsgi interface, and twisted can be used to serve wsgi applications. this is actually the ideal method for having the two interact with each other (and is the first post in this tutorial that runs 100% counter to my disclaimer)
detailed documentation for this process is available at the twisted documentation site http://twistedmatrix.com/documents/current/web/howto/web-in-60/wsgi.html
give a shot to modifying your current tutorial code to make this work.
there are two components required to properly serve the django portions of this tutorial as wsgi resources:
- configuring Django to work as twisted wsgi resource
- serving the static components of django through twisted
this is slightly more complicated than it sounds, since, in newer versions, django dynamically searches through an ordered list of directories when serving its static components. using twisted to mimic that same functionality can take some work. i opted to use a custom directory scanning twisted resource
there aren’t very many decisions to make here; most of the work has to do with reading the documentation, and figuring out how to access the specific, relevant interfaces. if you’re stuck, you can find a clear example here; this basic resource might help, too.
tried it? given up? since i’ll be relying on this work when expanding the tutorial, it might be worth your time to see how i did it (and see if it makes sense to you). take a look at this commit/diff to get a list of the specific changes i made – let me know if it makes sense (or if i made a mistake/have a typo)
the git repository for the ongoing chat tutorial has this completed step tagged as v.0.2.1 – if you’ve already cloned the git repo, you can check out a clean version like so:
git checkout v0.2.1
detecting anagrams in python
Aside
what’s the shortest anagram detector you know how to write, in python?
this is one that keeps feeling like it should be a one liner (because it’s very similar to this one liner), but i suspect can’t be done in one line
highlight to see a solution.
def fn(x,y):
if len(x) != len(y):
return False
for i in x:
y = y.replace(i,'',1)
return not len(y) > 0
PS: there’s a cool method for solving this for a fixed alphabet, using primes
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whyfore chat, with django, twisted and websockets?
Aside
upon seeing the work i’ve put into writing tutorials, showing how to get realtime chat working in django + twisted/websockets, you might make the assumption that i consider this architecture to be, in general, a good idea.
A.
twisted’s implementation of websockets is, as of this writing, not integrated into the main branch.
don’t use code that isn’t considered, by its authors, to be reliable enough to merge into and release as part of their application distribution.
B.
twisted is an event-driven networking engine
django is a solid, easy to use web framework
websockets, a tcp based protocol, is usually implemented as a strange mix between the tcp and http protocols
it is, generally speaking, not a good idea to mix abstraction levels; adding event-driven components to your application by combining twisted and django is a bad architectural decision. I strongly suggest you consider using twisted.web instead of mixing django and twisted.
websockets are a strange mix of protocols, and can be difficult to work with unless you are very careful with your choice of libraries and application design, scope and implementation. at the time of this post, i would recommend against using websockets, in production, with the standard deployment of twisted. i strongly urge you to consider the following alternatives, in rough order of likelihood to work for you:
- use autobahn
- look into using tornado. for example, try tornado + socketio. it’s probably your best alternative, if you’ve come this far
- look into using socket.io (eg, for django)
- look into pywebsocket
riddle 9 (python)
Aside
python riddle
def fn():
x = "Who's on first"
def f(y):
return x+y
x = "What's on second"
return f("?")
print fn()
(ok, so this is more of a mnemonic to help me remember how python works)
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riddle 7 (python)
Aside
python riddle
def listMutator(arglist):
arglist = ["mutated"]
print "arglist: ", arglist
test = ["not mutated"]
listMutator(test)
print "test: ", test
Bonus question – when is the following statement True, and when is it False?
-7/6 == -(7/6)
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project euler problem #8
Aside
Find the greatest product of five consecutive digits in the following 1000-digit number:
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450
http://projecteuler.net/problem=8
highlight below for my solution:
a_string = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"
print max([reduce(lambda x, y : x * y, [int(x) for x in a_string[i:i+5]])
for i in range(len(a_string) - 5)
])
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project euler problem #6
Aside
The sum of the squares of the first ten natural numbers is,
12 + 22 + … + 10^2 = 385
The square of the sum of the first ten natural numbers is,(1 + 2 + … + 10)^2 = 552 = 3025
Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 − 385 = 2640.Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.
http://projecteuler.net/problem=6
highlight below for my solution:
# A = (sum[1..n])^2 = [n(n+1)/2] ^ 2
# B = sum[1^2..n^2] = n(n+1)(2n+1)/6
# A-B = n(n+1)(3n^2-n-2)/12
def delta_sum_products_product_sum(n):
return n * (n + 1) * (3 * (n ** 2) - n - 2) / 12
print delta_sum_products_product_sum(100)
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riddle 6 (python)
Aside
python riddle
what do you expect will happen if you type this at the python prompt under python 2? python 3?
try:
range(0,5,"1")
except ValueError, TypeError:
print "this code has an error in it"
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ferretfarmer 