Pycon India 2013 talk

Author: pythonhacker

pyconindia2013/.ipynb_checkpoints/idiomatic_workshop-checkpoint.ipynb

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

pyconindia2013/examples/caching.py

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

pyconindia2013/examples/decorator.py

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

pyconindia2013/examples/grouping.py

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

pyconindia2013/examples/indent.py

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

pyconindia2013/examples/itertools_examples.py

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

pyconindia2013/examples/matrix.py

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

pyconindia2013/examples/primes.py

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

pyconindia2013/examples/selectors.py

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