Re: how to read the last line of a huge file???
I've implementing this method of reading a file from the end, i.e def seeker(filename): offset = -10 with open(filename) as f: while True: f.seek(offset, os.SEEK_END) lines = f.readlines() if len(lines) >= 2: return lines[-1] offset *= 2 and consistently run into the following error message when Python 3.2 (running under Pyscripter 2.4.1) tries to execute the line f.seek(offset,2) UnsupportedOperation: can't do non-zero end-relative seeks But offset is initialized to -10. Does anyone have any thoughts on what the error might be caused by? Thanks in advance Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Re: how to read the last line of a huge file???
Thanks for the pointer. Yes, it is a text file, but the mystery runs deeper: I later found that it works perfectly as written when I run it from IDLE or the Python shell, but it fails reliably when I run it from PyScripter 2.4.1 (an open source Python IDE)! So I suspect there's a PyScripter issue lurking in here. I'm next going to try the solution you propose - use only for legal offsets - and then retry it under both IDLE and PyScripter. Question: how do I use f.tell() to identify if an offset is legal or illegal? Thanks in advance Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Re: how to read the last line of a huge file???
There is a problem, and it's a Python 3.2 problem. All the solutions presented here work perfectly well in Python 2.7.1, and they all fail at exactly the same point in Python 3.2 - it's the line that tries to seek from the end. e.g. f.seek(offset, os.SEEK_END) I'll register this as a Python bug. Thank you, everyone, for the help and guidance. Sincerely Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Python 3.2 bug? Reading the last line of a file
The following function that returns the last line of a file works perfectly well under Python 2.71. but fails reliably under Python 3.2. Is this a bug, or am I doing something wrong? Any help would be greatly appreciated. import os def lastLine(filename): ''' Returns the last line of a file file.seek takes an optional 'whence' argument which allows you to start looking at the end, so you can just work back from there till you hit the first newline that has anything after it Works perfectly under Python 2.7, but not under 3.2! ''' offset = -50 with open(filename) as f: while offset > -1024: offset *= 2 f.seek(offset, os.SEEK_END) lines = f.readlines() if len(lines) > 1: return lines[-1] If I execute this with a valid filename fn. I get the following error message: >>> lastLine(fn) Traceback (most recent call last): File "", line 1, in lastLine(fn) File "", line 13, in lastLine f.seek(offset, os.SEEK_END) io.UnsupportedOperation: can't do nonzero end-relative seeks Sincerely Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 3.2 bug? Reading the last line of a file
Thanks for the guidance - it was indeed an issue with reading in
binary vs. text., and I do now succeed in reading the last line,
except that I now seem unable to split it, as I demonstrate below.
Here's what I get when I read the last line in text mode using 2.7.1
and in binary mode using 3.2 respectively under IDLE:
2.7.1
Name31/12/2009 0 0 0
3.2
b'Name\t31/12/2009\t0\t0\t0\r\n'
if, under 2.7.1 I read the file in text mode and write
>>> x = lastLine(fn)
I can then cleanly split the line to get its contents
>>> x.split('\t')
['Name', '31/12/2009', '0', '0', '0\n']
but under 3.2, with its binary read, I get
>>> x.split('\t')
Traceback (most recent call last):
File "", line 1, in
x.split('\t')
TypeError: Type str doesn't support the buffer API
If I remove the '\t', the split now works and I get a list of bytes
literals
>>> x.split()
[b'Name', b'31/12/2009', b'0', b'0', b'0']
Looking through the docs did not clarify my understanding of the
issue. Why can I not split on '\t' when reading in binary mode?
Sincerely
Thomas Philips
--
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Re: Python 3.2 bug? Reading the last line of a file
This is exactly what I want to do - I can then pick up various elements of the list and turn them into floats, ints, etc. I have not ever used decode, and will look it up in the docs to better understand it. I can't thank everyone enough for the generous serving of help and guidance - I certainly would not have discovered all this on my own. Sincerely Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Working with databases (ODBC and ORMs) in Python 3.2
We are in the process of trying to decide between Python 2.7 and 3.2 with a view to making a 5-10 year commitment to the right platform, and would appreciate some guidance on how best to connect to SQL databases in 3.2. ceODBC 2.01 provides an ODBC driver for Python 3.2, does anyone have experience using it? Also, are there any ORMs (object relational mapper)s that work well with 3,2? Thanks in advance Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Re: Q: "Best" book for teaching
I taught myself Python from Python Programming for the Absolute Beginner by Michael Dawson (which has been mentioned above) and with lots of help from the friendly members of this group, but there's now a free e-book titled Snake Wrangling for Kids by Jason Briggs. You can view it at http://www.briggs.net.nz/log/writing/snake-wrangling-for-kids/. There are versions for Windows, Mac and Linux, though it is focused on Python 2.x. Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Uploading files to an an FTP site through a proxy server which requires authentication
I would like to upload files to a ftp site, but can't seem to get through our proxy server, which requires authentication. How can one do this in Python (I use 2.7, but am more than happy to use 3.2 rc2) Thanks in advance Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Startup problems with Python 3.1.2 and PythonPath under XP
I run Python under Windows XP SP3, and for the longest time, I have installed it on my C: drive under C:\PythonXX (XX = 20, 21., 26), and maintained all my Python files on our network in a directory called H:\Python that I point to by creating an environment variable called PYTHONPATH. I recently installed 3.1.2 under C:\Python31, and now IDLE crashes every single time Python 3.1 starts up. If I remove PYTHONPATH, it starts up without a problem. The mystery deepens - Python 2.6 starts without a hiccup with or without PYTHONPATH! What could the issue be? Is there any other way to have H:\Python appended to sys.path when I start Python 3.1? Thank you in advance for your help and advice Thomas Philips -- http://mail.python.org/mailman/listinfo/python-list
Re: Startup problems with Python 3.1.2 and PythonPath under XP
I fixed the problem by creating a file call MyPath.pth that has only one line H:/Python and placing it in the C:\Python31\Lib\site-packages directory. So as a practical matter, my problem is solved. That said, I'm still puzzled by why Python 3.1 acts up when I set the environment variable PYTHONPATH. It certainly caused no problem with the 2.X series. -- http://mail.python.org/mailman/listinfo/python-list
Problems with extra blank line when using csv.writer in Python 3.1
I’m experiencing a problem with the csv module in Python 3.1.2, and
would greatly appreciate any help anyone can offer me. When writing
csv files in Python 2.6, I open the output file as 'wb' to prevent a
blank line being inserted after every line. Works like a charm. But I
get an error if I do the same in 3.1; i.e if type the following
sequence of commands:
>>> import csv
>>> outfile = open('c:/temp/test.csv', 'wb')
>>> writer = csv.writer(outfile)
>>> line = [1, 2, 3, 4]
>>> writer.writerow(line)
Traceback (most recent call last):
File "", line 1, in
writer.writerow(line)
TypeError: must be bytes or buffer, not str
Switching to
>>> outfile = open('c:/temp/test.csv', 'w')
makes it work, but I now have a blank line after each line when I open
the file using Excel. Any thoughts or guidance on what I ought to be
doing in 3.1 to fix the extra blank line problem?
Thank you in advance
Thomas Philips
--
http://mail.python.org/mailman/listinfo/python-list
Re: Problems with extra blank line when using csv.writer in Python 3.1
Worked like a charm! Thank you very much. -- http://mail.python.org/mailman/listinfo/python-list
Re: python needs a tutorial for install and setup on a Mac
I think a setup guide for the Mac would prove very useful. Earlier this year, I tried installing Python 2.6 on my iMac, and ran into all sorts of problems, largely as a result of the fact that I knew very little about Unix. I finally downloaded and installed the Enthought Python distribution for the Mac and it worked like a charm. -- http://mail.python.org/mailman/listinfo/python-list
