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Title: Lambda, Enumerate and List comprehensions crash
Type: crash Stage: resolved
Components: Interpreter Core Versions: Python 2.7
process
Status: closed Resolution: not a bug
Dependencies: Superseder:
Assigned To: Nosy List: ned.deily, wilsoncampusano
Priority: normal Keywords:

Created on 2014年07月26日 02:00 by wilsoncampusano, last changed 2022年04月11日 14:58 by admin. This issue is now closed.

Files
File name Uploaded Description Edit
test_c.py wilsoncampusano, 2014年07月26日 02:00 code that crash
test_c.py wilsoncampusano, 2014年07月26日 02:15 Code that crash
Messages (3)
msg224015 - (view) Author: wilson campusano (wilsoncampusano) * Date: 2014年07月26日 02:00
SO: Ubuntu 14.04
When i run this code my pc crash
msg224017 - (view) Author: wilson campusano (wilsoncampusano) * Date: 2014年07月26日 02:15
SO: Ubuntu 14.04
When i run this code my pc crash
msg224018 - (view) Author: Ned Deily (ned.deily) * (Python committer) Date: 2014年07月26日 02:46
It may be hard to see what's going on with the code written as a list comprehension. We could expand it out to something roughly equivalent and print the first n iterations:
def main():
 lista =[1, 4, 5 , 5, 6 , 3 ,1]
 def ins(x):
 return lista.insert(x,0)
 for idx, v in enumerate(lista):
 if v == 5:
 ins(idx)
 print(idx, lista)
 if idx > 10:
 break
if __name__ == '__main__':
	main()
(2, [1, 4, 0, 5, 5, 6, 3, 1])
(3, [1, 4, 0, 0, 5, 5, 6, 3, 1])
(4, [1, 4, 0, 0, 0, 5, 5, 6, 3, 1])
(5, [1, 4, 0, 0, 0, 0, 5, 5, 6, 3, 1])
(6, [1, 4, 0, 0, 0, 0, 0, 5, 5, 6, 3, 1])
(7, [1, 4, 0, 0, 0, 0, 0, 0, 5, 5, 6, 3, 1])
(8, [1, 4, 0, 0, 0, 0, 0, 0, 0, 5, 5, 6, 3, 1])
(9, [1, 4, 0, 0, 0, 0, 0, 0, 0, 0, 5, 5, 6, 3, 1])
(10, [1, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 5, 6, 3, 1])
(11, [1, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 5, 6, 3, 1])
Because the list is mutating by inserting the 0 before the 5, once the 5 entry is found, it keeps "moving" to the right so the loop never terminates and lista keeps expanding until Python runs out of memory. Don't do that!
History
Date User Action Args
2022年04月11日 14:58:06adminsetgithub: 66273
2014年07月26日 02:46:41ned.deilysetstatus: open -> closed

nosy: + ned.deily
messages: + msg224018

resolution: not a bug
stage: resolved
2014年07月26日 02:15:00wilsoncampusanosetfiles: + test_c.py

messages: + msg224017
2014年07月26日 02:11:22wilsoncampusanosettitle: Lambda, enumerate and list comprehensins crash -> Lambda, Enumerate and List comprehensions crash
2014年07月26日 02:00:11wilsoncampusanocreate

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