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Loop structure of program (for loop)
2022-07-06 01:13:00 【Leifeng】
Traversal cycle :for loop
Traversal cycle refers to the cycle operation mode formed by traversing a certain structure :
for < Loop variable > in < Traversal structure >:
< Sentence block >
Every time I cycle , Extract one of the elements from the traversal structure , Put it in the previous loop variable , Execute the following statement block , After performing , Then extract the next element from the traversal structure , When all elements in the traversal structure are put into the loop variable , And all have been executed circularly , So the program exits .
Extract elements one by one from the traversal structure , Put it in a loop variable , Then execute the following statement block
By reserved words for and in form , Complete traversal of all elements ends
Each cycle , The resulting element is placed in a loop variable , And execute the statement block once
The traversal structure used is a structure that can contain multiple elements , The so-called traversal structure is not a special type , It contains many types .
Count cycle (N Time ):
for i in range(N):
< Sentence block >
His execution effect is to traverse the following statement block , perform N Content of secondary statement block .
Traversal by range() Function produces a sequence of numbers , Create a cycle .
for Sentences can be compared with range() Function collocation ,range() Function can generate an iteratable object composed of integers ( It can be simply understood as supporting the use of for Loop traversed objects ),range(N) The function generates a sequence of numbers , This sequence contains N Elements , Each element is an integer , Namely 0,1 Until N-1
Count cycle N Time , We can use this variable in the middle i, It is also possible not to use variables i, about for in range It's a cycle N Time , As for not using intermediate loop variables, it is decided according to the logic of the program .
The code example is as follows :
for i in range(5): print(i)
The operation interface is as follows :
Count cycle ( Specific times ):
The format is as follows :
for i in range(M,N,K):
from M Start , Less than N, To N Previous integer , With K Step length .
The code of example 1 is as follows :
for i in range(1,6):# from 1 Start , To 6 Previous integer 5 print(i)
The operation interface is as follows :
The code of example 2 is as follows :
for i in range(1,6,2):# from 1 Start , To 6 Previous integer 5, With 2 Step length . print(i)
The operation interface is as follows :
String traversal loop :
for c in s:
< Sentence block >
s Is string , Traverses each character of the string , Create a cycle .
c Represents each character in the string , It can take each character out of the string in order and put it in c in , And for each extracted character , Execute the statement block once , And create a cycle .
The code example is as follows :
for c in "Python123": print(c,end=",")
The operation interface is as follows :
List traversal loop :
for item in ls:
< Sentence block >
ls It's a list , Traverse every element of it , Create a cycle
The code example is as follows :
for item in [123,"PY",456]: print(item,end=",")
The operation interface is as follows :
Tuple traversal loop :
for i in ( Elements ):
print(i)
The code is as follows :
for i in ('python',1,5,6): print(i)
The operation interface is as follows :
Dictionary traversal loop :
Output all elements in the following format :
dic={' ' : ,' ': }
for item in dic.items():
print(item)
The code is as follows :
dic={'python':1,'age':27,5:6} for item in dic.items(): print(item)
The operation interface is as follows :
Output all keys in the following format :
dic={' ' : ,' ': }
for item in dic.keys():
print(item)
The code is as follows :
dic = {'python': 1, 'age': 27, 5: 6} for item in dic.keys(): print(item)
The operation interface is as follows :
Output the values corresponding to all keys :
dic={' ' : ,' ': }
for item in dic.values():
print(item)
The code is as follows :
dic = {'python': 1, 'age': 27, 5: 6} for item in dic.values(): print(item)
The operation interface is as follows :
The traversal loop uses reserved words for in A cycle formed , It can assign the current loop variable to each element in the traversal structure , And form a cycle .
all for in Such a traversable structure , As long as the following variables or this data type , It is a data type composed of multiple elements , You can use for in The way , Traverse every element of it , And according to the number of elements , Form a corresponding cycle .
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