An example Analysis of the list statement of python interview questions
This article mainly introduces the python interview list statement example analysis, the article is very detailed, has a certain reference value, interested friends must read it!
The details are as follows:
What is the output of the following program?
val = [['a']*2]*2print valval[0][1]='b'print val
The answer is:
[['a', 'a'], ['a', 'a']]
[['a', 'b'], ['a', 'b']]
rather than
[['a', 'a'], ['a', 'a']]
[['a', 'b'], ['a', 'a']]
Consider the following example:
val = ['a']*2 #or simply declare val = [' a','a'] print valid (val)print id(val[0])print id(val[1])
The output is
['a', 'a']
39993928
38858384
38858384
You can see that the two 'a's in val point to the same address:
Look at the following code:
A direct statement does not change the subsequent 'a'
val = [['a','a'],['a','a']]print valprint id(val)print id(val[0][0])print id(val[1][0])val[0][0] = 'b'print valprint id(val)print id(val[0][0])print id(val[1][0])
The results are:
[['a', 'a'], ['a', 'a']]
39405512
38268560
38268560
[['b', 'a'], ['a', 'a']]
39405512
38390280
38268560
and
val = [['a','a']]*2print valprint id(val)print id(val[0][0])print id(val[1][0])val[0][0] = 'b'print valprint id(val)print id(val[0][0])print id(val[1][0])
The results are:
[['a', 'a'], ['a', 'a']]
40388552
39251600
39251600
[['b', 'a'], ['b', 'a']]
40388552
39373320
39373320
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