Python has some very clever and powerful built-in functions, which are generally not used by beginners. I only discovered after using python for a while, wow, there is such a good thing. Function, this function is classic and has been rigorously tested. It can save you a lot of things at once. The code is not only more concise and easy to read, but also you don’t have to create it behind closed doors. It is convenient for you and reduces the cost. Bug. 1.sorted()
1) For sorting a listsorted([100, 98, 102, 1, 40])
>>>[1, 40, 98, 100, 102]
For example, there are many dictionary elements nested in a long list. We need to sort according to the length of each element
L = [{1:5,3:4},{1:3,6:3},{1:1,2:4,5:6},{1:9}] new_line=sorted(L,key=lambda x:len(x)) print(new_line) >>>[{1: 9}, {1: 5, 3: 4}, {1: 3, 6: 3}, {1: 1, 2: 4, 5: 6}]
For example, the following is a list of the ages of students
students = [('wang', 'A', 15), ('li', 'B', 12), ('zhang', 'B', 10)] print(sorted(students, key=lambda student : student[2])) >>>[('zhang', 'B', 10), ('li', 'B', 12), ('wang', 'A', 15)]
students = [('wang', 'A', 15), ('li', 'B', 12), ('zhang', 'B', 10)]
print(sorted(students, cmp=lambda x,y : cmp(x[0], y[0])) )
>>>[('li', 'B', 12), ('wang', 'A', 15), ('zhang', 'B', 10)]
2.map()
, and applies the function f to each element on the list, and then returns A new list, the input parameters of the map function can also be multiple. Note that this function must have a return value (the value is important three times). Otherwise, a new list will be returned, similar to [None, None, None, None, None, None, None, None, None]
Suitable The scenario requires repeated operations on some elements in the list, which can be easily done with map.
3.enumerate()
is always taken out The element itself, not the index of the element. Sometimes we need to know the index of the element. For example, there are some website names in a long list. We hope that the index can also be listed when printing. If there is no such function, we need to add a variable and increment the counting variable when printing in the loop. Now that we have enumerate, we don’t have to go to such trouble. We can do it directly.
4.zip()
x = [1, 2, 3] y = [4, 5, 6] z = [7, 8, 9] xyz = zip(x, y, z) >>print xyz
This function is especially useful in building dictionary sequences It is very convenient (this trick is very clever, you can carefully
figure it out)
##5.filter()
filter function accepts A function f and a list. The function of this function f is to judge each element and return True or False. This cando not meet the conditions , and then return Qualified list.
def is_even(x): return x%2==0 print(filter(is_even,[1,2,3,4,5])) >>>[2, 4]
6.reduce()
Note that reduce in python3
has been removed from the global function. If you need to use it, pleasefrom functools import reduceFinally, I insist on originality. If what I write is helpful to everyone, please Everyone encourage
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