Ramesh Sahoo added the comment:
Hi all,
Thanks for your valuable response. I would like to inform you that I found this
issue while playing with the following code. This is reproducible with Python
3.8.
Please find the following details and let me know if I am doing something
wrong.
[Using for loop popping elements]
import sys
stack,braces = [],{'(':')','{':'}','[':']'}
stack = [s for s in "(([])"]
c = 0
print(f"Python version: {sys.version}")
print(f"Before for loop:\nbraces.keys = {braces.keys()}\nbraces.items =
{braces.items()}\nstack = {stack}\n\n")
for i in stack:
c += 1
print(f"{'='*10} loop {c} {'='*10}")
print("just after for loop stack =",stack)
print(f"Just after for loop i =",i)
print(f"Just after for loop: Is i'{i}' found in braces.keys:{i in
braces.keys()}")
if i in braces.keys():
print(f"inside if i = {i}")
print("inside if stack =",stack)
print("inside if Popped =",stack.pop(stack.index(i)))
print(f"inside if after popped stack = {stack}\n")
continue
else:
print(f"in else: Is i'{i}' found in braces.keys:{i in braces.keys()}")
print(f"in else stack = {stack}\n")
[Program Output]
$ python3 test1.py
Python version: 3.8.0 (default, Nov 14 2019, 22:29:45)
[GCC 5.4.0 20160609]
Before for loop:
braces.keys = dict_keys(['(', '{', '['])
braces.items = dict_items([('(', ')'), ('{', '}'), ('[', ']')])
stack = ['(', '(', '[', ']', ')']
== loop 1 ==
just after for loop stack = ['(', '(', '[', ']', ')']
Just after for loop i = (
Just after for loop: Is i'(' found in braces.keys:True
inside if i = (
inside if stack = ['(', '(', '[', ']', ')']
inside if Popped = (
inside if after popped stack = ['(', '[', ']', ')']
== loop 2 ==
just after for loop stack = ['(', '[', ']', ')']
Just after for loop i = [
Just after for loop: Is i'[' found in braces.keys:True
inside if i = [
inside if stack = ['(', '[', ']', ')']
inside if Popped = [
inside if after popped stack = ['(', ']', ')']
== loop 3 ==
just after for loop stack = ['(', ']', ')']
Just after for loop i = )
Just after for loop: Is i')' found in braces.keys:False
in else: Is i')' found in braces.keys:False
in else stack = ['(', ']', ')']
[Summary]
stack = ['(', '(', '[', ']', ')']
=> [loop 1] is correct where the right element "(" has been popped.
['(', '[', ']', ')']
=> [loop 2] "(" element should have been popped but "[" chosen to be popped.
This seems to be incorrect.
=> There must be 5 iterations(3 in if block and 2 in else block) but loop
completed with 3 iterations(2 in if and one in else).
I am not sure if I am doing something wrong or it is a buggy behavior.
[Popping elements manually gives correct behavior]
import sys
print(f"Python Version: {sys.version}")
stack,braces = [],{'(':')','{':'}','[':']'}
stack = [s for s in "(([])"]
print(f"Original:\nbraces.keys = {braces.keys()}\nbraces.items =
{braces.items()}\nstack = {stack}\n\n")
# Popping '('
print(f"Popped {stack.pop(stack.index('('))}")
print(f"stack after popping '(' = {stack}")
# Popping '('
print(f"Popped {stack.pop(stack.index('('))}")
print(f"stack after popping '(' = {stack}")
# Popping '['
print(f"Popped {stack.pop(stack.index('['))}")
print(f"stack after popping '[' = {stack}")
[Program Output]
Python Version: 3.8.0 (default, Nov 14 2019, 22:29:45)
[GCC 5.4.0 20160609]
Original:
braces.keys = dict_keys(['(', '{', '['])
braces.items = dict_items([('(', ')'), ('{', '}'), ('[', ']')])
stack = ['(', '(', '[', ']', ')']
Popped (
stack after popping '(' = ['(', '[', ']', ')']
Popped (
stack after popping '(' = ['[', ']', ')']
Popped [
stack after popping '[' = [']', ')']
--
status: closed -> open
versions: +Python 3.8 -Python 3.6
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