Some common Python methods compiled for your reference

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

The above is the detailed content of Some common Python methods compiled for your reference. For more information, please follow other related articles on the PHP Chinese website!