Iteration and looping in python

The commonly used loop structure is the for statement used to iterate multiple items. Loops are one of the most important functions of python. The most common iteration is just to loop through all members of a sequence (string, list, or tuple)
1, iterate the list:

for n in [1,2,3,4,5,6,7,8,9]:  
 print("number:%d  value: %d" %(n,2*n))

Output result:

number:1 value: 2
number:2 value: 4
number:3 value: 6
number:4 value: 8
number:5 value: 10
number:6 value: 12
number:7 value: 14
number:8 value: 16
number:9 value: 18

Explanation: Each iteration will assign the value in the list to the variable n. It is very common to perform loops within the integer range. , a shortcut method was produced for this:

for n in range(1,10):  
 print("number:%d value:%d"%(n,2*n));

Output result:

number:1 value:2
number:2 value:4
number:3 value:6
number:4 value:8
number:5 value:10
number:6 value:12
number:7 value:14
number:8 value:16
number:9 value:18

range(i,j) The object range created by the range(i,j) function ranges from i to j-1 If starting If omitted, the starting value is considered to be 0. The third parameter is an optional step value:

a = range(10);  
b = range(1,6);  
c = range(0,10,2)

Output result

0,1,2,3,4,5,6,7,8,9
1,2,3,4,5
0,2,4,6,8 #步进值

If you are using python3.0 or below For version, you can try to use the xrange() method, which was renamed range() after python3.0
The range method also exists in PHP and is similar to the usage in python
2 Iterate string

a  = "Hello World"   
for c in a :  
 print(c); #打印出字符串中的所有字符

3, iterate element Group

name = ('小旋风柴进','美髯公朱仝','行者武松','混江龙李俊');  
for nm in name:  
 print(nm);

Output result:

小旋风柴进
美髯公朱仝
行者武松
混江龙李俊

4, iterate dictionary

data = {  
 'name' : '张三',  
 'age' : 18,  
 'addr' :'北京',  
 'price' :1800  
}

Output result:

name 张三
age 18
price 1800
addr 北京

5, iterate all files Line

f = open('e:/work.txt');  
for line  in f:  
 print(line); #循环输出文件中所有行

Output result:

'tom',120,132
'jon',234,255
'jeck',123,678

Loop iteration in php:
1, for loop

for($i=0;$i<=10;$i++){  
 echo $i . &#39;,&#39;;  
}

Explanation: $i=0 The starting value of the loop; $iOutput results:
0,1,2,3,4,5,6,7,8,9,10
can also be used to loop strings:

$str = 'Hello world';  
for($i=0;$i<strlen($str);$i++){  
 echo $str[$i].&#39;,&#39;;  
}

Explanation: strlen is the method used to obtain the string length in the string method in php
Output results:
H,e,l,l,o, ,w,o,r,l,d
2, foreach Loop: There is no concept of tuples, lists and dictionaries in PHP, but there is the concept of array. The foreach statement is used to loop through the array.
1. Index array: The digital index automatically assigned by the system or added manually

$arr = array(1,2,3,4,5,6,7);  
  
$value = 0;  
  
foreach($arr as $v){  
  
 $value += $v;  
  
}

echo $value;

Output result:

28

$arr = array("one",'two','three');  
  
foreach($arr as $k=>$v){  
  
 echo &#39;key:&#39;.$k .&#39;value:&#39;.$v.&#39;<br/>&#39;;  
  
}

Output result:

key:0value:one
key:1value:two
key:2value:three

2 Associative array: use custom keys

$arr = array('name'=>'张三','age'=>18,'addr'=>'北京');  
  
foreach($arr as $k=>$v){  
  
 echo $k.'='.$v.',';  
  
}

Output result:
name =Zhang San,age=18,addr=Beijing
Summary:
1, this section describes the most commonly used method of iteration in python is for...in... loop
2, for.. .in iteration is used to print data in lists, tuples, dictionaries, and text in a loop
3, compare with the for loop statement and foreach loop statement in PHP

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