Detailed explanation of python for and while loops

Original January 21, 2017 12:06:12

Label:
python /
while /
for /
cycle

for loop

1. For statement format

for expression 1 in expression 2: # Determine whether expression 1 is in the range included in expression 2

Statement 1 # If the previous condition is true, execute the following statement

Statement 2

...

statement n

Two, for loop example

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number = [ 1 , 2 , 3 , 4 , 5 ]               # create a list called number  
for  i  in  number:                   # Determine whether the variable i is included in the number list  
           print "The number is %d"   %i       # Print if included.      

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<span> </span> # After the execution is completed, return to the beginning of the for statement to continue to judge whether the condition is true;  

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Note:  The judgment statement in the for  loop can use the undefined variable i  

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<span> </span> In fact, the variable is defined at the beginning of the for loop, and will be redefined every time the loop begins;  

while loop

First, the while statement format

while Judgment condition: # If the judgment condition is true, the execution statement in the loop body is executed; The judgment condition is true can be any expression, any non-zero, non-null (null) value;

execute statement

2. While example

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#!/usr/bin/python  
#-*-  coding:UTF-8  -*-  
  
i =  0 # Create a variable named i and assign the initial value to 0;                        

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numbers = range( 0 , 6 )      # Wear a list named numbers and assign it with the range function;  

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whilie i <  5 :             # First judge whether the expression i < 5 is true; if it is true, execute the statement in the loop body;  

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print   numbers[i]   # print the i+1th element of the list number, (the table below of the list starts from 0);  

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<span style= "white-space:pre;" > </span>i = i+ 1 # Increment the variable by 1;             

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Summarize

>>> Try to use less while loops, most of the time for loops are better

>>> for loop is used to match a specific set and loop # similar to the switch case statement in C language;

>>> while loop is used to judge the condition is true and loop

>>>

appendix

Learning and Reference Links

(1) python tutorial: http://www.runoob.com/python/python-while-loop.html

(2) python online programming website: https://penjee.com/tutorial