[issue14542] reverse() doesn't reverse sort correctly
New submission from Bill Jefferson : reverse() doesn't reverse sort correctly in Python 25 and 27. sort() works correctly, but reverse doesn't. The following uses reverse(). Incorrect. Even though the date comes first, reverse() sorts on the file name, "B57IBMCD_T.zip" 2012-04-05 B57IBMCD_T7.2.3.1.zip 2012-03-23 B57IBMCD_T7.2.2.3.zip 2012-02-22 B57IBMCD_T7.2.2.2.zip 2012-02-13 B57IBMCD_T7.2.2.1.zip 2012-01-23 B57IBMCD_T7.2.1.1.zip 2012-03-28 B57IBMCD_T7.0.4.6.zip 2012-03-08 B57IBMCD_T7.0.4.5.zip 2012-03-03 B57IBMCD_T7.0.4.4.zip 2012-02-29 B57IBMCD_T7.0.4.3.zip 2012-01-06 B57IBMCD_T7.0.4.2.zip 2011-12-08 B57IBMCD_T7.0.4.1.zip 2012-01-06 B57IBMCD_T7.0.3.1.zip 2012-01-06 B57IBMCD_T7.0.2.2.zip 2012-01-06 B57IBMCD_T7.0.2.1.zip 2012-01-06 B57IBMCD_T6.2.4.9.zip 2011-12-07 B57IBMCD_T6.2.4.9-r1.zip 2011-09-13 B57IBMCD_T6.2.4.8.zip 2012-03-28 B57IBMCD_T6.2.4.12.zip 2012-02-15 B57IBMCD_T6.2.4.11.zip 2011-12-06 B57IBMCD_T6.2.4.10.zip -- components: Demos and Tools, IDLE, Windows files: EX38.PY messages: 157988 nosy: billje priority: normal severity: normal status: open title: reverse() doesn't reverse sort correctly type: performance versions: Python 2.7 Added file: http://bugs.python.org/file25172/EX38.PY ___ Python tracker <http://bugs.python.org/issue14542> ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue14542] reverse() doesn't reverse sort correctly
Bill Jefferson added the comment:
Eric.
Thanks for answering, but I don't understand the difference between "reversing
a list" and "reversing it's current values". If I have a list containing
elements: A, B, C, D and reverse the list's current values, I get: D, C, B, A,
which is the same as reversing the list. Please explain in more detail. Perhaps
you can recommend good reference material. Since sort() sorts a list ascending
(and works correctly), shouldn't reverse() sort the list descending? Am I using
the wrong function? I have attached my program:
Bill.
#EX38.PY Get listing of all files in a directory
#http://stackoverflow.com/questions/237079/how-to-get-file-creation-modification-date-times-in-python
# Answer 37
import os, datetime
topDir = "C:/BrcmCDs"
dateFirst = True # put dates before file names
# DateFirst = False # put file names before dates
def modDate(fileN): # returns a 10-place date string
t = os.path.getmtime(directory+"/"+fileN)
return str(datetime.datetime.fromtimestamp(t))[0:10]
for directory, dirnames, filenames in os.walk(topDir):
outList = []
print "Directory: ", directory
print
for fileA in filenames:
if (fileA[0:10] == "B57IBMCD_T" and
fileA[-4:] == ".zip"):
dateString = modDate(fileA)
if dateFirst:
fileString = dateString + " " + fileA
else:
fileString = fileA + " " + dateString
outList.append(fileString)
outList.sort() # sort the file list, ascending
# outList.reverse() # reverse the file list, desending
print outList #show all files
# now save list to a file:
# https://bbs.archlinux.org/viewtopic.php?id=75839
f = open("fileList.TXT", "w")
f.write("\n".join(map(lambda x: str(x), outList)))
f.close()
Regards from:
William Jefferson Photography
514 Daniels St., #211
Raleigh, NC 27605
Cell Phone: (919) 931-6681
EMail: shagge...@yahoo.com
Brides & Weddings: http://www.WilliamJeffersonPhotography.com
Special Events: http://www.DancingLight.org
From: Eric V. Smith
To: shagge...@yahoo.com
Sent: Tuesday, April 10, 2012 5:45 PM
Subject: [issue14542] reverse() doesn't reverse sort correctly
Eric V. Smith added the comment:
list.reverse() does not reverse a list, it reverses its current values.
Help on built-in function reverse:
reverse(...)
L.reverse() -- reverse *IN PLACE*
>>>
--
nosy: +eric.smith
resolution: -> invalid
stage: -> committed/rejected
status: open -> closed
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[issue14542] reverse() doesn't reverse sort correctly
Bill Jefferson added the comment: Mark and Eric.. Wonderful! I got it now. I used x.sort(reverse=True) and x.sort(reverse=False) and it works just fine. Thanks for your help. Bill.. Regards from: William Jefferson Photography 514 Daniels St., #211 Raleigh, NC 27605 Cell Phone: (919) 931-6681 EMail: shagge...@yahoo.com Brides & Weddings: http://www.WilliamJeffersonPhotography.com Special Events: http://www.DancingLight.org From: Mark Dickinson To: shagge...@yahoo.com Sent: Wednesday, April 11, 2012 8:28 AM Subject: [issue14542] reverse() doesn't reverse sort correctly Mark Dickinson added the comment: Bill, list.reverse doesn't do any *sorting* at all; it merely *reverses* the list contents. [2, 4, 3, 1] If you want to do a reverse sort, you can either first sort normally and then reverse the result, or (easier) use the 'reverse' keyword argument to the list.sort method, as follows: [4, 3, 2, 1] I suspect Eric meant to write "does not reverse sort" instead of "does not reverse". -- nosy: +mark.dickinson ___ Python tracker <http://bugs.python.org/issue14542> ___ -- ___ Python tracker <http://bugs.python.org/issue14542> ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
