| msg46132 - (view) |
Author: Relm Arrowny (relm) |
Date: 2004-06-07 09:45 |
| You can test for the first line of a file with fileinput.isfirstline(), but there is no corresponding fileinput.islastline() to test for the last line of a file. Note that there is already an unapplied patch for this at request ID 776100, but it is faulty in that it only tests for end of buffer and not end of file. I was not sure how to append this patch to the existing request, so have started a new one. Hope this is okay. This patch also includes documentation and test updates. |
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| msg46133 - (view) |
Author: Raymond Hettinger (rhettinger) *  |
Date: 2004-06-15 12:05 |
| Logged In: YES user_id=80475 I'm -0 on complicating this venerable interface. Also, I find it unnatural for the inside of a loop to be able to ascertain whether it is in its final iteration. The closest approximation is the for-else clause which is vary rarely used in normal python programming. While the OP was able to sketch a use case, it involved only saving a couple of lines over what can be done with the existing API. |
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| msg46134 - (view) |
Author: Relm Arrowny (relm) |
Date: 2004-06-15 18:42 |
| Logged In: YES user_id=1058331 The OP's use case was too simplified to convey the usefulness of fileinput.islastline(). It does not just save a couple of lines. I am attaching a "wc" or "word count" program to demonstrate. Note the following problems with the current work-around: 1. Instead of doing end-of-file processing at the end of a file, we must do it at the beginning of the *next* file. 2. Useful functions such as fileinput.filelineno() and fileinput.filename() now refer to the *wrong* file, so now we need to manually keep track of these values ourselves. 3. Perhaps a minor point, but this work-around only works at the *beginning* of the loop instead of the end. It feels somewhat awkward. 4. End-of-file processing must occur both in the loop and once outside. A function avoids code duplication, but to refer to variables in the loop, they must be passed into and out of the function (6 in, 2 out for the "wc" example... maybe keyword arguments would have helped). 5. Most important is readablility. It's not obvious that `fileinput.isfirstline() and fileinput.lineno() != 1` means we are the end of the (previous!) file. Using `fileinput.islastline()` would be much clearer. And not that it is a reason, but Perl and Ruby solve this with an `eof` function and `eof?` method, respectively. |
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| msg46135 - (view) |
Author: Dave Harrison (dharriso) |
Date: 2004-07-04 11:24 |
| Logged In: YES user_id=1076674 I would say that I'm -0.5 on this feature. After looking over the current code for fileinput.py in the cvs tree, it looks like the current code implements an iterator model. Since fileinput.py uses the next() call to move along its input, and raises StopIteration if there are no more lines to be returned, this function would have to be polled to find out if the final line had been reached - where a try/except block that caught StopIteration would seem more intuitive to me (Inkeeping with the current code). However it might be considered that the nextfile() function be changed to raise StopIteration after the last file had been completed to maintain consistency between the lines and files aspects of the class. |
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| msg46136 - (view) |
Author: Ilya Sandler (isandler) |
Date: 2004-08-05 18:17 |
| Logged In: YES user_id=971153 An alternative to islastline() would be to add a single-line look-ahead capability: nextline() which would return a structure containing next line, and its file name (or have 2 functions nextline() and nextlinefile() ) This would cover most of the OP's needs but would also provide extra useful functionality....E.g. when processing files which have a header line [data line]* structure its very convenient to know in advance when section ends while processing the last line of section not when enountering the header line of the next section... Another use case would be processing of files with line groups: group1line1 group1line2 group1line3 group2line1 group2line2 (grouping could be for example on the value of a certian field in the line) again it would be very useful to know when a group ends while still processing this group |
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| msg46137 - (view) |
Author: Björn Lindqvist (sonderblade) |
Date: 2007-03-14 01:25 |
| I have applied this patch and it works as specified. Although it does not apply cleanly and it contains an error; self._lastline = None should probably be in the __init__() method. Please reconsider this patch and see Relms attached wc program. It is definitely sensible and useful for fileinput to have a islastline method. In fact, every program that uses fileinput and wants to make a summary for each read file. |
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| msg81711 - (view) |
Author: Daniel Diniz (ajaksu2) *  |
Date: 2009-02-12 02:58 |
| Issue issue 776100 closed as duplicated. |
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| msg125560 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2011-01-06 15:49 |
| Anyone wants to produce an up-to-date patch for py3k? |
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| msg129609 - (view) |
Author: Dj Gilcrease (Digitalxero) |
Date: 2011-02-27 03:22 |
| Updated the patch and tests for py3.3 |
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| msg137209 - (view) |
Author: Éric Araujo (eric.araujo) * |
Date: 2011-05-29 17:34 |
| Would storing len(self._buffer) in the instance be premature optimization? |
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| msg187432 - (view) |
Author: Mark Lawrence (BreamoreBoy) * |
Date: 2013-04-20 14:57 |
| The latest patch still applies cleanly, can we have it reviewed please. |
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| msg286385 - (view) |
Author: Saurav Singh (damngamerz) |
Date: 2017-01-27 21:26 |
| last patch works fine i have applied and tested the patch.Its documented well.Can we please have it reviewed? |
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| msg287069 - (view) |
Author: Berker Peksag (berker.peksag) * |
Date: 2017-02-06 02:47 |
| Thanks for the updated patch, but I'm not sure FileInput class needs a islastline() method. I couldn't find any similar or duplicate feature requests on the tracker after this opened in 2004 (which is a sign that the need for this method is low.) Also, the patch needs some work. Some comments: * There is no documentation changes to Doc/library/fileinput.rst * 'mark' is unused in Lib/fileinput.py * Not sure why we need 't1 = t2 = t3 = None' in tests * We could use self.addCleanup() instead of 'try...finally' * fileinput.islastline() is not tested. We could reuse Test_fileinput_isfirstline. According to commit history of Lib/fileinput.py, Serhiy has done a lot of work in the past few years. I just added him to nosy list to get his feedback. |
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| msg287080 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-02-06 06:15 |
| The patch is outdated. It uses private _buffer attribute which no longer exist (see ). But even when _buffer was existing the patch was not correct, because _buffer contained only a part of the file. It is possible to implement islastline(), but at the cost of additional buffering. This effectively negates the result of . The user would need to enter two lines first than fileinput could return the fist one from stdin. And additional complication slows down reading for all users even if they don't need islastline(). If you need islastline() you can use a wrapper: def yield_line_and_islastline(f): try: prevline = next(f) except StopIteration: return for line in f: yield (prevline, f.isfirstline()) prevline = line yield prevline, True |
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| msg292601 - (view) |
Author: John Tapsell (John Tapsell) |
Date: 2017-04-29 20:12 |
| > If you need islastline() you can use a wrapper: This doesn't work because fileinput.filename() and fileinput.filelineno() are going to be wrong and pointing to the next file. |
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| msg416576 - (view) |
Author: Irit Katriel (iritkatriel) * |
Date: 2022-04-02 18:53 |
| > This doesn't work because fileinput.filename() and fileinput.filelineno() are going to be wrong and pointing to the next file. You won't have this problem if you work on one file at a time. |
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| msg416577 - (view) |
Author: Irit Katriel (iritkatriel) * |
Date: 2022-04-02 18:54 |
| I am closing this as the discussion ended in 2017 with something like three +0s. Please raise this for discussion on python-ideas if you would like to pursue it further. |
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