python 101 language features and functional programming

SHOCKING

Reverse String – JavaScriptvar s = "This is the simple text object";

var r = "";for (var i = s.length - 1; i >= 0 ;

i--) {r += s[i];

}function reverse (s) {

return (s === '''') ? : reverse(s.substr(1)) + s.charAt(0);}

Reverse String – Java

String s = "This is the test";System.out.println(new StringBuilder(s).reverse().toString());

Reverse String – PHP

echo strrev("Hello World");

Reverse String – Python

s[::-1]

Find element in array

var zipCodes = (['90001','90002','90003']);

if ( zipCodes.indexOf('9005') > -1 ) { console.log("found") ;} else {

console.log("not Found");}

JavaScript

Find element in array

HashMap<Integer,String> cities = new HashMap<Integer, String>();cities.put(9000,"Gent");cities.put(9400,"Aalst");

String city = cities.get(9400);System.out.println(city);

Java

Find element in arrayPHP

$array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');

$key = array_search('green', $array); // $key = 2;$key = array_search('red', $array); // $key = 1;

$os = array("Mac", "NT", "Irix", "Linux");

if (in_array("Irix", $os)) {    echo "Got Irix";}

Find element in array

element in data

Python

Design Principles• Borrow ideas whenever it make sense• As simple as possible , not simpler (Einstein)• Do one thing well (Unix)• Don’t fret abut performance (fix it later)• Don’t bother user with details• Error shouldn’t pass silently

Numbers

i = 45f = 3.14l = 23Lc = 2 + 4j

oct(78)hex(78)bin(-3)

a=int('01100000',2)b=int('00100110',2)bin(a&b) # '0b100000'bin(a|b)# '0b1100110'bin(a^b) # '0b1000110'

Data Structure - String

s = " The snake is LONG, 7 miles "

len(s)s.count("is")s.endswith("miles ")s.swapcase()s.strip()s.index("7", 5, 22)

Operations:

"A" + "b"

"snake" in s

"kilo meters" not in s / not "kilo meters" in s

s * 2

Data Structure – List (Array)

l = [ 3, 4, 0, 0, 5, 2, 1]k = [ 1, 2, 3, 4,5]

len(l)l.count(0)l.remove(0)l.index(4)l.append(55)

Operations:k + ll * 23 not in k / not 3 in k

0 1 2 3 4 5+---+---+---+---+---+---+| a | b | c | d | e | f |+---+---+---+---+---+---+ -6 -5 -4 -3 -2 -1

Data Structure – Dictionary http://svn.python.org/view/python/trunk/Objects/dictobject.c?view=markup&pathrev=53656a = dict(one=1, two=2, three=3)b = {'one': 1, 'two': 2, 'three': 3}c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))d = dict([('two', 2), ('one', 1), ('three', 3)])e = dict({'three': 3, 'one': 1, 'two': 2})

>>> a == b == c == d == e

d.items()d.keys()d.values()

Operations:

d.update(d2)

one in b

1 in a.values()

Data Structure – Tuple (Immutable)

t = ("a", "b", "c", "d")

t.count()t.index()

Operations:t * 2t + t"a" in t "a" not in t

Data Structure – Set (Immutable)

a = set([1,2,3]) b = set([2,3,4])

a.union(b)a.intersection(b)a.difference(b)

Operations:1 in s5 not in s

Files / Picklef = open("D:/foo.txt", "wb")

f.write("My python is longer than yours. ")

f.close()

import pickle

output = [1,2 "a", "b", "c"]

f = open('data.pk’, 'wb')

pickle.dump(output, f)

f.close()

pickle.load(open('data.pk', 'rb'))

Comprehension / Generator (Haskell)

simplifies process of iterationswords = 'The quick brown fox jumps over the lazy dog'.split()

[[word.upper(), word.lower(), len(word)] for word in words]

matrix = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]

[[row[i] for row in matrix] for i in range(4)] # list comprehension

g = ([ row[i] for row in matrix ] for i in range(4)) # generator

Functions and F.Programming

def f1():return "function One!"

def f2():return "function Two!"

d = {"one" : f1, "two" : f2}

d["one"]()d["two"]()

FUNCTIONAL PROGRAMMINGIterators

http://www.youtube.com/watch?v=Ta1bAMOMFOIhttp://ua.pycon.org/static/talks/kachayev/#/28

Your Father:x = [1, 2, 3]

y = ["a", "b", "c"]

[(i,j) for i in x for j in y]

The Dude:x = [1, 2, 3]

y = ["a", "b", "c"]

t = zip(x,y)

dict(zip(x,y))

Iterators:it = iter(t)

dict(it)

FUNCTIONAL PROGRAMMING (LiSP)

"Lazy programmer is good programmer“ map(), filter(), reduce(), enumerate()

def up(x): return

x.upper()

map(up, ["a", "test"])

def even(x): if (x % 2) == 0:

return x

filter(even, [1, 2, 3, 4, 5, 6, 7, 8])

import operator

reduce(operator.add, [1,2,3])

for item in enumerate(["a", "b","c"]) print item

Lamb-daaaaahttp://www.youtube.com/watch?v=_WZwp16c4vk

FUNCTIONAL PROGRAMMINGhttp://ua.pycon.org/static/talks/kachayev/#/28

f = lambda x: x * 2f(2)

g = lambda x, y: x + yg(2,2)

lambs = [lambda x: x ** 2,

lambda x: x ** 3, lambda x: x ** 4]

for f in lambs: f(3)

Lambda + F.P. Functionsmap(lambda x: x.upper(), ["a", "test"])

filter(lambda x: (x % 2) == 0, [1,2,3,4,5,6,7,8])

[x for x in 'abracadabra' if x not in 'abc']{x for x in 'abracadabra' if x not in 'abc'}

sorted(d.items(), key=lambda i: i[1])pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]pairs.sort(key=lambda pair: pair[1])