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Pycon India 2013 talk
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‎pyconindia2013/.ipynb_checkpoints/idiomatic_workshop-checkpoint.ipynb

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‎pyconindia2013/examples/caching.py

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""" Caching decorator example """
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def cache(f):
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results = {}
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def wrapper(*args):
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if args in results:
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print 'From cache'
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return results[args]
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res = f(*args)
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results[args] = res
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return res
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return wrapper
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@cache
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def factorial(n):
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""" Factorial of a number """
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return reduce(lambda x,y: x*y, range(1,n+1))
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if __name__ == "__main__":
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print factorial(5)
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print factorial(10)
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print factorial(5)

‎pyconindia2013/examples/decorator.py

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""" Simple decorator for type checking """
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def isNumber(f):
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def wrapper(*args):
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if not all(type(item) in (int, float) for item in args):
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raise TypeError,'Wrong type!'
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return f(*args)
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return wrapper
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@isNumber
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def add(x,y):
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return x+y
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@isNumber
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def mul(x,y):
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return x*y
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if __name__ == "__main__":
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print add(3, 4)
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print mul(5,6)
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add(4, 'me')

‎pyconindia2013/examples/grouping.py

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""" Grouping with dictionaries """
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import collections
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fruit_bag = ['apple','grapes','apple','mango','mango','apple',
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'banana','orange','guava','sapota','apple','orange',
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'litchi','strawberry','lemon','apple','grapes']
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def group_solution_a():
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fruit_group = {}
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for fruit in fruit_bag:
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if fruit not in fruit_group:
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fruit_group[fruit] = 0
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fruit_group[fruit] += 1
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return fruit_group
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def group_solution_b1():
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fruit_group = {}
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for fruit in fruit_bag:
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fruit_group[fruit] = fruit_group.get(fruit, 0) + 1
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return fruit_group
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def group_solution_b2():
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fruit_group = collections.defaultdict(int)
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for fruit in fruit_bag:
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fruit_group[fruit] += 1
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return fruit_group
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if __name__ == "__main__":
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print group_solution_a()
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print group_solution_b1()
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print group_solution_b2()

‎pyconindia2013/examples/indent.py

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""" Indenting context manager """
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from contextlib import contextmanager
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spaces = 0
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@contextmanager
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def indent():
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global spaces
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spaces += 1
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print '\t'*spaces,
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yield
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spaces -= 1
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class Indent(object):
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def __init__(self):
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self.spaces = 0
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def __enter__(self):
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self.spaces += 1
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print '\t'*self.spaces,
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def __exit__(self, type, value, traceback):
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self.spaces -= 1
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if __name__ == "__main__":
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for i in range(2,5):
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with indent():
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print 'This is number',i
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with indent():
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print 'This is its square',i*i
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for i in range(2,5):
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indenter = Indent()
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with indenter:
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print 'This is number',i
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with indenter:
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print 'This is its square',i*i
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‎pyconindia2013/examples/itertools_examples.py

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""" Itertools examples """
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import itertools
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import collections
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import operator
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import os
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# itertools.count can provide an infinite counter.
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for i in itertools.count(step=1):
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print i
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if i == 20: break
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# itertools.cycle cycles through an iterator
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# Will keep printing 'python'
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for i,j in enumerate(itertools.cycle(['python'])):
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print j
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if i==10: break
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# itertools.repeat keeps repeating from an iterator
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# Will keep producing range(10) when called in a loop
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print itertools.repeat(range(10))
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# chain returns elements from 'n' iterators until they are exhausted.
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# Make a dictionary of count of letters in a list of strings.
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birds = ['parrot','crow','dove','peacock','macaw','hen']
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frequency = collections.defaultdict(int)
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for letter in itertools.chain(*birds):
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frequency[letter] += 1
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print frequency
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# takewhile returns elements as long as a predicate(condition) is True.
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# Give list of favorable countries
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countries=['U.S','U.K','India','Australia','Malaysia','Pakistan']
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print list(itertools.takewhile(lambda x: x != 'Pakistan', countries))
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# dropwhile keeps dropping elements while predicate is True.
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# Produce iterator of files > a minimum size in current folder.
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files = sorted([(file, os.path.getsize(file)) for file in os.listdir(".")],
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key=operator.itemgetter(1))
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print list(itertools.dropwhile(lambda x: x[1] < 8192, files))

‎pyconindia2013/examples/matrix.py

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""" Matrix class as an example for zip to transpose lists """
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import random
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class MatrixA:
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def __init__(self,m,n):
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self.m, self.n = m,n
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self.rows=[[random.randrange(1,10) for j in range(n)] for i in range(m)]
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def __str__(self):
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s='\n'.join([' '.join([str(item) for item in row]) for row in self.rows])
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return s + '\n'
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def transpose(self):
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rows2 = [[0]*self.m for i in range(self.n)]
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for x in range(self.m):
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for y in range(self.n):
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rows2[y][x] = self.rows[x][y]
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self.rows = rows2
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# Swap m and n
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tmp = self.m
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self.m = self.n
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self.n = tmp
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class MatrixB(MatrixA):
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def transpose(self):
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self.m, self.n = self.n, self.m
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self.rows = zip(*self.rows)
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if __name__ == "__main__":
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m = MatrixA(3,4)
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print m
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m.transpose()
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print m
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m = MatrixB(3,4)
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print m
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m.transpose()
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print m

‎pyconindia2013/examples/primes.py

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""" Prime number generation """
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import random
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from itertools import cycle,imap,dropwhile,takewhile
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def is_prime(n):
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""" Is the number 'n' prime ? """
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prime = True
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for i in range(2,int(pow(n,0.5))+1):
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if n % i==0:
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prime = False
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break
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return prime
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def prime_solution_a(n):
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count, numbers = 0, []
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while count<n:
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num = random.randrange(1,1000)
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if num not in numbers and is_prime(num):
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numbers.append(num)
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count += 1
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return numbers
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def prime_solution_b(n):
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sieve = lambda n: not any(n % num==0 for num in range(2, int(pow(n,0.5))+1))
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nums = set()
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for i in takewhile(lambda x:len(nums)<=20,
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dropwhile(sieve,imap(random.randrange,cycle([1]),
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cycle([100])))):
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nums.add(i)
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return nums
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if __name__ == "__main__":
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print prime_solution_a(20)
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print prime_solution_b(20)

‎pyconindia2013/examples/selectors.py

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""" Selecting values from an iterable using multiple conditions """
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import itertools
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import collections
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cutoffs = {'maths': 40, 'elec': 35,
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'lab' : 45, 'cs': 30,
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'phy' : 25, 'chem': 35}
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marks_dict = { 'Karan': {'maths': 39, 'elec': 78, 'cs': 83,
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'lab': 32, 'phy': 60, 'chem': 91},
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'Arjun': {'maths': 49, 'elec': 45, 'lab': 53,
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'cs': 43, 'phy': 86, 'chem': 54},
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'Rancho': {'maths': 86, 'elec': 85, 'cs': 95,
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'lab': 83, 'phy': 91, 'chem': 75},
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'Raju': {'maths': 32, 'elec': 36, 'lab': 50,
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'cs': 26, 'phy': 35, 'chem': 41},
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'Farhan': {'maths': 30, 'elec': 56, 'cs': 21,
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'lab': 33, 'phy': 27, 'chem': 56}}
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def find_passed(marks_dict,cutoffs):
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# Initialize dictionary
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pass_dict = {subject:[] for subject in cutoffs}
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for subject, cutoff in cutoffs.iteritems():
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for student, student_marks in marks_dict.iteritems():
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if student_marks[subject] >= cutoff:
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pass_dict[subject].append(student)
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return pass_dict
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def find_passedi(marks_dict, cutoffs):
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# defaultdict
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pass_dict = collections.defaultdict(list)
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# Dict comprehensions
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selectors = {(subject, student) :cutoffs[subject]<=val[subject] for subject in cutoffs for student,val in marks_dict.items()}
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# itertools compress
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passd = list(itertools.compress(selectors.keys(), selectors.values()))
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for subject,student in passd:
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pass_dict[subject].append(student)
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return pass_dict
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if __name__ == "__main__":
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passd = find_passed(marks_dict, cutoffs)
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print 'Passed =>',passd
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passd = find_passedi(marks_dict, cutoffs)
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print 'Passed =>',passd

‎pyconindia2013/examples/sentinel.py

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""" Checking for sentinel values """
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from itertools import takewhile,imap,cycle
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import functools
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import random
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def solution_a(sentinel):
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# Solution A
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# Append numbers till you hit sentinel
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nums = []
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while True:
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num = random.randrange(1, 100)
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if num == sentinel: break
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nums.append(num)
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return nums
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def solution_b1(sentinel):
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func = functools.partial(random.randrange, 1, 100)
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nums = []
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for num in iter(func, sentinel):
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nums.append(num)
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return nums
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def solution_b2(sentinel):
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return list(takewhile(lambda x: x!=sentinel,
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imap(random.randrange, cycle([1]), cycle([100]))))
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if __name__ == "__main__":
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print solution_a(41)
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print solution_b1(41)
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print solution_b2(41)

‎pyconindia2013/examples/timing.py

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""" Timing tests for punctuation replace functions """
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from itertools import imap, chain, ifilter
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from functimer import functimer
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import string
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import re
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punc = string.punctuation
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def repl_listcomp(strings):
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return [''.join(i for i in s if i not in punc) for s in strings]
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def repl_functional(strings):
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return map(lambda x: ''.join(i for i in x if i not in punc),strings)
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def repl_itertools1(strings):
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return list(imap(lambda x: ''.join(i for i in x if i not in punc),strings)
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def repl_itertools2(strings):
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return ''.join(ifilter(lambda x: x not in punc, chain(*strings)))
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def repl_re(strings):
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return [re.sub('[' + punc + ']+', '', x) for x in strings]
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if __name__ == "__main__":
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strings = ['#I love,@,#',' PyCon India..$#,']
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print 'Listcomp =>',functimer(repl_listcomp, strings)
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print 'Functional =>',functimer(repl_functional, strings)
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print 'Itertools #1 =>',functimer(repl_itertools1, strings)
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print 'Itertools #2 =>',functimer(repl_itertools2, strings)
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print 'Re =>',functimer(repl_re, strings)

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