Pickling recursion error, did not import pickle

[Octopi]

BPO	44379
Nosy	@terryjreedy, @serhiy-storchaka

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-06-10.23:11:29.753>
created_at = <Date 2021-06-10.15:31:07.006>
labels = ['invalid', 'expert-IDLE', 'type-bug', '3.8', '3.10']
title = 'Pickling recursion error, did not import pickle'
updated_at = <Date 2021-06-10.23:11:29.752>
user = 'https://bugs.python.org/Octopi'

bugs.python.org fields:

activity = <Date 2021-06-10.23:11:29.752>
actor = 'terry.reedy'
assignee = 'none'
closed = True
closed_date = <Date 2021-06-10.23:11:29.753>
closer = 'terry.reedy'
components = ['IDLE']
creation = <Date 2021-06-10.15:31:07.006>
creator = 'Octopi'
dependencies = []
files = []
hgrepos = []
issue_num = 44379
keywords = []
message_count = 3.0
messages = ['395542', '395552', '395587']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'serhiy.storchaka', 'Octopi']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44379'
versions = ['Python 3.8', 'Python 3.10']

[Octopi]

I accidentally created an infinite recursion. The error referenced pickling but I did not import pickle.

To reproduce:
def permute(inputList):
'''permute(inputList) -> list
returns list of all permutations of inputList
CURRENTLY DOESN'T ACTUALLLY WORK PROPERLY'''
for i in range(len(inputList)-1):
tempList = inputList[:-i-2]
tempList.append(inputList[-1])
for num in inputList[-i-2:-1]:
tempList.append(num)
print(tempList)
permute(tempList) # runs infinitely (whoops)
print()

permute([1,2,3,4])

Error thrown: 
Traceback (most recent call last):
  File "C:\Users\Violet\Documents\Python Files\test.py", line 14, in <module>
    permute([1,2,3,4])
  File "C:\Users\Violet\Documents\Python Files\test.py", line 11, in permute
    permute(tempList)  # runs infinitely (whoops)
  File "C:\Users\Violet\Documents\Python Files\test.py", line 11, in permute
    permute(tempList)  # runs infinitely (whoops)
  File "C:\Users\Violet\Documents\Python Files\test.py", line 11, in permute
    permute(tempList)  # runs infinitely (whoops)
  [Previous line repeated 1009 more times]
  File "C:\Users\Violet\Documents\Python Files\test.py", line 10, in permute
    print(tempList)
RecursionError: maximum recursion depth exceeded while pickling an object

[serhiy-storchaka]

It is because you run the code in IDLE.

print(tempList) converts argument to string and write it to sys.stdout. In IDLE sys.stdout is a proxy object which uses RPC to communicate with the IDLE process which should insert the written text in the console text widget. Pickle is used for encoding command and arguments. Here you get a recursion error in pickle because when print(tempList) is executed the recursion depth almost reached the limit.

[terryjreedy]

The 'while pickling' part of the message is specific to running in IDLE, as Serhiy explained, but the recursion error itself is due to writing a program with infinite recursion. The program switches the last two items back and forth indefinitely. When run directly in Python, it gives the same error, with a different 'while' part.

Violet, this tracker is for patching Python docs and the CPython interpreter. Please ask questions about program behavior elsewhere, such as python-list.