Python の学習: Python に関する 17 のヒント

"""pythonic way of value swapping""" a, b=5,10 print(a,b) a,b=b,a print(a,b)

a=["python","is","awesome"] print(" ".join(a))

"""most frequent element in a list""" a=[1,2,3,1,2,3,2,2,4,5,1] print(max(set(a),key=a.count)) """using Counter from collections""" from collections import Counter cnt=Counter(a) print(cnt.most_commin(3))

from collections import Counter Counter(str1)==Counter(str2)

"""reversing string with special case of slice step param""" a ='abcdefghij k lmnopqrs tuvwxyz 'print(a[ ::-1] ) """iterating over string contents in reverse efficiently.""" for char in reversed(a): print(char ) """reversing an integer through type conversion and slicing .""" num = 123456789 print( int( str(num)[::1]))

"""reversing list with special case of slice step param""" a=[5,4,3,2,1] print(a[::1]) """iterating over list contents in reverse efficiently .""" for ele in reversed(a): print(ele )

"""transpose 2d array [[a,b], [c,d], [e,f]] -> [[a,c,e], [b,d,f]]""" original = [['a', 'b'], ['c', 'd'], ['e', 'f']] transposed = zip( *original ) print(list( transposed) )

""" chained comparison with all kind of operators""" b =6 print(4< b < 7 ) print(1 == b < 20)

"""calling different functions with same arguments based on condition""" def product(a, b): return a * b def add(a, b): return a+ b b =True print((product if b else add)(5, 7))

"""a fast way to make a shallow copy of a list""" b=a b[0]= 10 """ bothaandbwillbe[10,2,3,4,5]""" b = a[:]b[O] = 10 """only b will change to [10, 2, 3, 4, 5] """ """copy list by typecasting method""" a=[l,2,3,4,5] print(list(a)) """using the list.copy( ) method ( python3 only )""" a=[1,2,3,4,5] print(a.copy( )) """copy nested lists using copy. deepcopy""" from copy import deepcopy l=[l,2],[3,4]] l2 = deepcopy(l) print(l2)

""" returning None or default value, when key is not in dict""" d = ['a': 1, 'b': 2] print(d.get('c', 3))

"""Sort a dictionary by its values with the built-in sorted( ) function and a ' key' argument .""" d = {'apple': 10, 'orange': 20, ' banana': 5, 'rotten tomato': 1) print( sorted(d. items( ), key=lambda x: x[1])) """Sort using operator . itemgetter as the sort key instead of a lambda""" from operator import itemgetter print( sorted(d. items(), key=itemgetter(1))) """Sort dict keys by value""" print( sorted(d, key=d.get))

"""else gets called when for loop does not reach break statement""" a=[1,2,3,4,5] for el in a: if el==0: break else: print( 'did not break out of for loop' )

"""converts list to comma separated string""" items = [foo', 'bar', 'xyz'] print (','.join( items)) """list of numbers to comma separated""" numbers = [2, 3, 5, 10] print (','.join(map(str, numbers))) """list of mix data""" data = [2, 'hello', 3, 3,4] print (','.join(map(str, data)))

"""merge dict's""" d1 = {'a': 1} d2 = {'b': 2} # python 3.5 print({**d1, **d2}) print(dict(d1. items( ) | d2. items( ))) d1. update(d2) print(d1)

"""Find Index of Min/Max Element . """ lst= [40, 10, 20, 30] def minIndex(lst): return min( range(len(lst)), key=lst.. getitem__ ) def maxIndex(lst): return max( range( len(lst)), key=lst.. getitem__ ) print( minIndex(lst)) print( maxIndex(lst))

"""remove duplicate items from list. note: does, not preserve the original list order""" items=[2,2,3,3,1] newitems2 = list(set( items)) print (newitems2) """remove dups and, keep. order""" from collections import OrderedDict items = ["foo", "bar", "bar", "foo"] print( list( orderedDict.f romkeys(items ).keys( )))