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This article mainly introduces some common methods and techniques in the collection of Python. This article explains three methods of reversing strings, four methods of traversing a dictionary, and traversing a list Three methods, dictionary sorting method, etc. Pythoncommon tips and methods, friends in need can refer to the following
1. Three methods of reversing strings
1.1. Simulate the method in C++, define an empty string to achieve
By setting an empty string, and then traverse the string in the parameter from back to front, using string addition Merge into a new string
def reverse(text) : str = '' index = len(text) - 1 while index >= 0 : str += text[index] index -= 1 return str
1.2. Use the slicing method
This is a feature in Python. Slicing can take negative values. This is the method of using slicing. , set the step size to -1, thus achieving reverse sorting.
def reverse_1(text) : return text[::-1]
1.3. Using a list
Use the reverse method of the list, first convert the text into a list, then reverse it through the reverse method, and then connect it into characters through join string.
def reverse_2(text) : temp = list(text) temp.reverse() return ''.join(temp)
2. Use reduce
Use anonymous function and reduce()
def reverse_3(text) : return reduce(lambda x, y : y + x, text) print reverse_3("Hello")
3. Traverse the dictionary Four methods of
dict={"a":"apple","b":"banana","o":"orange"} print "##########dict######################" for i in dict: print "dict[%s]=" % i,dict[i] print "###########items#####################" for (k,v) in dict.items(): print "dict[%s]=" % k,v print "###########iteritems#################" for k,v in dict.iteritems(): print "dict[%s]=" % k,v print "###########iterkeys,itervalues#######" for k,v in zip(dict.iterkeys(),dict.itervalues()): print "dict[%s]=" % k,v
4. Three methods of traversing list
for key in lst : print key for i in range(len(lst)) : print lst[i] for index, key in enumerate(lst) : print key //index是list的索引
5. Method of dictionary sorting
The dictionary is sorted according to the value of value from large to small (default is sorted from small to small).
dic = {'a':31, 'bc':5, 'c':3, 'asd':4, 'aa':74, 'd':0} dict= sorted(dic.iteritems(), key=lambda d:d[1], reverse = True) print dict //输出的结果: [('aa', 74), ('a', 31), ('bc', 5), ('asd', 4), ('c', 3), ('d', 0)]
Let’s decompose the code below
print dic.iteritems() to get a list of [(key, value)].
Then use the sorted method, through the key parameter, to specify that the sorting is based on value, that is, the value of the first element d[1. reverse = True means that it needs to be flipped. The default is from small to large. If it is flipped, it will be from large to small.
Sort dictionary by key:
dic = {'a':31, 'bc':5, 'c':3, 'asd':4, 'aa':74, 'd':0} dict= sorted(dic.iteritems(), key=lambda d:d[0]) # d[0]表示字典的键 print dict #sorted中第三个可选参数为reverse, True表示从大到小排序 #默认reverse = False
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