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Some common Python methods compiled for your reference

伊谢尔伦
伊谢尔伦Original
2017-06-28 13:36:591109browse

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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