for cycle time pop phenomenon

= A [ ' A ' , ' B ' , ' C ' , ' D ' ,. 1, 2,. 3, 4,5,6,7,8 ]
 for index, X in the enumerate (A):
     Print ( " Index is {}, {} is the length of the list, delete the values {} " .format (index, len (a), a [-1 ])) 
    a.pop () 
    Print (a) 

    Print ( " = " * 20 is ) 

Print ( ' ~~~~~ ' ) 

A2 = [ ' A ' ,'b','c','d',1, 2, 3, 4,5,6,7,8]
for i in a2:
    a2.pop()
    print(a2)

`~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`

/usr/local/bin/python3.7 /code/pop2.py
index is 0, the length of the list is 12, the value is deleted. 8
[ 'A', 'B', 'C', 'D',. 1, 2, 3, 4, 5, 6, 7]
====================
index is 1, the length of the list is 11, the value is deleted 7
[ 'a ',' B ',' C ',' D ',. 1, 2,. 3,. 4,. 5,. 6]
====================
index is 2, length of the list is 10, the value is deleted. 6
[ 'a', 'B', 'C', 'D',. 1, 2,. 3,. 4,. 5]
============ ========
index is 3, the length of the list is 9, the value is deleted. 5
[ 'a', 'B', 'C', 'D',. 1, 2, 3,. 4]
== ==================
index is 4, the length of the list is 8, the value deleted is the 4
[ 'a', 'B', 'C', 'D', 1, 2, 3]
====================
index is 5, the length of the list 7, the value is deleted 3
[ 'a', 'B', 'c', 'd', 1,2]
====================
~~~~~
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5, 6, 7]
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5, 6]
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5]
['a', 'b', 'c', 'd', 1, 2, 3, 4]
['a', 'b', 'c', 'd', 1, 2, 3]
['a', 'b', 'c', 'd', 1, 2]

Process finished with exit code 0

Why the analysis, the final result is not pop [], but the [ 'a', 'b', 'c', 'd', 1, 2] is stopped.

Can look at the first code. When each iteration, the index values are accumulated when the time index is 5, pop has been deleted to [ 'a', 'b', 'c', 'd', 1 2] left 6., index values is six 0,1,2,3,4,5

Assuming that the index is 6, then the list of values which we need seven, but the results have not seven values in it. So it was suspended.

Therefore, if it continues to accumulate the index, the index is 6, the value of [ 'a', 'b', 'c', 'd', 1,] is the index values, but this in turn 0,1,2,3,4 only five values, the index only up to 4, so there is no index 6, only suspended.

================= Similarly ===================

= A [. 1, 2,. 3,. 4 ]
 for index, X in the enumerate (A):
     Print ( " index of {}, to delete the value of {} is the length of the list is {} " .format (index, X , len (A))) 
    a.remove (X) 
    Print ( " = " * 20 is )
 Print (A)

The results are as follows:

the index is 0, the value 1 is to be deleted, the length of the list is 4
====================
index is 1, the value is 3 to delete, 3 is the length of the list
====================
[2, 4]

If the index is 2, but the above [2,4], only to index 1, it is 0, 1. 2 index does not exist, therefore, only the results of the 2 and 4.

note:

Variation in length of the list, the index value is changing. This is easy to overlook one point, because the object is a for loop iteration may object.

Therefore, if the above list, recycled to [] may be solved by the following method.

= A2 [ ' A ' , ' B ' , ' C ' , ' D ' , 1,2,3,4,5,6,7,8 ] 

Print (len (A2)) 

for I in Range (len (A2 )):
     # del A2 [0] this method can also be, may be the following pop 
    a2.pop ()
     Print (A2)

/usr/local/bin/python3.7 /code/pop2.py
12
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5, 6, 7]
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5, 6]
['a', 'b', 'c', 'd', 1, 2, 3, 4, 5]
['a', 'b', 'c', 'd', 1, 2, 3, 4]
['a', 'b', 'c', 'd', 1, 2, 3]
['a', 'b', 'c', 'd', 1, 2]
['a', 'b', 'c', 'd', 1]
['a', 'b', 'c', 'd']
['a', 'b', 'c']
['a', 'b']
['a']
[]

Process finished with exit code 0

for cycle time pop phenomenon

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