New submission from Mark Summerfield:
In the attached file there are two tiny functions, flatten1() and
flatten2(). There is only one difference between them:
flatten1() has the line:
if isinstance(x, list):
and flatten2() has this line instead:
if isinstance(x, collections.Sequence):
flatten1() works perfectly in Python 2.5.1 and Python 30a2 (just comment
out the flatten2() code).
But flatten2() goes into "infinite" recursion in Python 30a2 when trying
to flatten list "c".
----------
components: Interpreter Core
files: bug.py
messages: 58536
nosy: mark
severity: normal
status: open
title: infinite recursion when using collections.Sequence in a recursive
function (Py30a2)
type: behavior
versions: Python 3.0
Added file: http://bugs.python.org/file8939/bug.py
__________________________________
Tracker <[EMAIL PROTECTED]>
<http://bugs.python.org/issue1612>
__________________________________
import collections
def flatten1(seq):
"""Returns a list containing all the items in seq with no nested
sequences
>>> a = [[1, 2], [3, [4, [5, 6], 7], 8], 9, [10, 11], [12]]
>>> b =flatten1(a)
>>> b
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
>>> flatten1(b) == b
True
>>> c = [["S"] * 4, ["M"] * 2, "R", "H", ["D"] * 3, "A", "B", "E"]
>>> flatten1(c)
['S', 'S', 'S', 'S', 'M', 'M', 'R', 'H', 'D', 'D', 'D', 'A', 'B', 'E']
"""
result = []
for x in seq:
if isinstance(x, list):
result.extend(flatten1(x))
else:
result.append(x)
return result
def flatten2(seq):
"""Returns a list containing all the items in seq with no nested
sequences
>>> a = [[1, 2], [3, [4, [5, 6], 7], 8], 9, [10, 11], [12]]
>>> b =flatten2(a)
>>> b
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
>>> flatten2(b) == b
True
>>> c = [["S"] * 4, ["M"] * 2, "R", "H", ["D"] * 3, "A", "B", "E"]
>>> flatten2(c)
['S', 'S', 'S', 'S', 'M', 'M', 'R', 'H', 'D', 'D', 'D', 'A', 'B', 'E']
"""
result = []
for x in seq:
if isinstance(x, collections.Sequence):
result.extend(flatten2(x))
else:
result.append(x)
return result
if __name__ == "__main__":
import doctest
doctest.testmod()
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