File Handling Problems Python I/O

[Josh]

Hi,

I am having a problem with Python. I am new to Python as a programming
language, but I do have experience in other languages. I am
experiencing strange problems with File handling and wonder if anyone
else has seen this or knows what I am doing wrong. I am simply trying
to open a file for read and iterate through until the end of file. I am
able to do so without a problem, but here's the catch: The open
statement is only working on certain files. I open a simple text file
say file1.txt without any issues, but I change the open statement to
another text file and it error's out stating the file doesn't exist. I
know the code is correct because it worked for the other file. I have
tried both binary and ascii modes to no avail. Any idea why this is
happening? I am running Python 2.3.4 wxPython 2.5.3.1 and SPE as the
IDE on Win2k. Thanks

Josh

[Arjen Dijkstra]

I don't think we can help if you don't post some of your code.

Regards,
Arjen

Josh wrote:

Hi,

I am having a problem with Python. I am new to Python as a programming
language, but I do have experience in other languages. I am
experiencing strange problems with File handling and wonder if anyone
else has seen this or knows what I am doing wrong. I am simply trying
to open a file for read and iterate through until the end of file. I am
able to do so without a problem, but here's the catch: The open
statement is only working on certain files. I open a simple text file
say file1.txt without any issues, but I change the open statement to
another text file and it error's out stating the file doesn't exist. I
know the code is correct because it worked for the other file. I have
tried both binary and ascii modes to no avail. Any idea why this is
happening? I am running Python 2.3.4 wxPython 2.5.3.1 and SPE as the
IDE on Win2k. Thanks

Josh

[Peter Hansen]

Josh wrote:

I am having a problem with Python. I am new to Python as a programming
language, but I do have experience in other languages. I am
experiencing strange problems with File handling and wonder if anyone
else has seen this or knows what I am doing wrong. I am simply trying
to open a file for read and iterate through until the end of file. I am
able to do so without a problem, but here's the catch: The open
statement is only working on certain files. I open a simple text file
say file1.txt without any issues, but I change the open statement to
another text file and it error's out stating the file doesn't exist.

The usual rookie mistake here is to fail to recognize
that backslashes in strings are interpreted as special
escape sequences if they precede certain characters such
as "t" or "b". You probably have a path that looks like
this: "c:\temp\myfile .txt", right? The \t is actually
being converted into a TAB character.

You can use *forward* slashes in most cases in Windows,
except on the command line. The simplest fix is just
to convert your backslashes to forward slashes:
"c:/temp/myfile.txt"

Another approach, somewhat less desirable, is to use
"raw" strings instead, to prevent the escape sequences from
being recognized:
r"c:\temp\myfil e.txt"

Finally, and by far least desirable, use double-backslashes
to escape each backslash and in effect nullify the usual
escape handling:
"c:\\temp\\myfi le.txt"

Much less readable that way, but sometimes the right thing to do...

-Peter

[Josh]

He is the function where I am making the call. If I change the open
statment to another file, say "c:\test.tx t", a file I know exists, it
will error out stating the file does not exist. Thanks

Josh

def GetStartVars(se lf):
try:
DOWNFILE = open("c:\fixes. txt","r")
except IOError:
print "Failed to open file."
else:
counter = 1
while 1:
theline = DOWNFILE.readli ne()
if not theline:
break
print theline
counter = counter + 1
print counter
DOWNFILE.close( )

[Josh]

Peter,

Thank you for the rookie correction. That was my exact problem. I
changed the address to use forward slashes and it works perfect. I did
not know that a backslash had special meaning within a string, but now
I do! Thanks again

Josh

[deelan]

Josh wrote:

Peter,

Thank you for the rookie correction. That was my exact problem. I
changed the address to use forward slashes and it works perfect. I did
not know that a backslash had special meaning within a string, but now
I do! Thanks again

you may want to check "python gotchas" to avoid
other typical newbie errors:

<http://www.ferg.org/projects/python_gotchas. html>

HTH,
deelan

--
"Vedrai come ti tratteranno le mie TV"
Berlusconi a Follini (Luglio 2004)

[Alex Martelli]

Josh <Jo**********@g mail.com> wrote:
...

He is the function where I am making the call. If I change the open
statment to another file, say "c:\test.tx t", a file I know exists, it

Are you sure a file exist whose name is, c, colon, tab, e, s, t ...?

\t is an escape sequence and it means TAB (character of ascii code 9).

Try 'c:/test.txt' -- using normal slash instead the backslash -- and you
should be fine.

You mention you have some experience with other languages: if those
languages include C, or Java, or C++, and many others besides (all which
use backslashes for escape sequences in strings), you'd have exactly the
same issues.
Alex

[mhartl]

You can use the os module to build path names in a platform-independent
manner. On my Linux box, I can type

BASE = '/'
import os
os.path.join(BA SE, 'foo', 'bar', 'baz') '/foo/bar/baz'

On a Windows machine, you get
BASE = 'C:'
import os
os.path.join(BA SE, 'foo', 'bar', 'baz')

'C:\\foo\\bar\\ baz'

This is a little more cumbersome that just typing the string, but using
os.path.join makes it easy to port your scripts to a new platform.
Check out http://docs.python.org/lib/module-os.path.html for more
information.
Cheers,

Michael

--
Michael Hartl
http://michaelhartl.org/

[mhartl]

Sorry, the BASE variable should be 'C:\\' on Windows:

BASE = 'C:\\'
import os
os.path.join(BA SE, 'foo', 'bar', 'baz')

'C:\\foo\\bar\\ baz'

[Josh]

Micheal,

Thanks for the advice as the programming I am doing will be run on both
Windows and Linux based PC's, that being the main reason for my venture
into Python. I'm glad to see that people are willing to help out even
the newbie's.

Josh