Basic file operation questions

[alex]

Hi,

I am a beginner with python and here is my first question:
How can I read the contents of a file using a loop or something? I open
the file with file=open(filen ame, 'r') and what to do then? Can I use
something like

for xxx in file:
....


Thanks for help
Alex

[Caleb Hattingh]

Re: Basic file operation questions

Hi Alex

Assuming you have a file called "data.txt":

***
f = open('data.txt' ,'r')
lines = f.readlines()
f.close()
for line in lines:
print line
***
Will print each line of the file.

You can make a huge investment by setting 2 or 3 hours aside to go through
the Python tutorial, which gets installed as part of the documentation.
That tutorial can get you much of the knowledge you will ever need with
Python.

thx
Caleb


On 2 Feb 2005 13:27:49 -0800, alex <alexander.diet z@mpi-hd.mpg.de> wrote:
[color=blue]
> Hi,
>
> I am a beginner with python and here is my first question:
> How can I read the contents of a file using a loop or something? I open
> the file with file=open(filen ame, 'r') and what to do then? Can I use
> something like
>
> for xxx in file:
> ....
>
>
> Thanks for help
> Alex
>[/color]

[Marcel van den Dungen]

Re: Basic file operation questions

alex wrote:[color=blue]
> Hi,
>
> I am a beginner with python and here is my first question:
> How can I read the contents of a file using a loop or something? I open
> the file with file=open(filen ame, 'r') and what to do then? Can I use
> something like
>
> for xxx in file:
> ....
>
>
> Thanks for help
> Alex
>[/color]
take a look at this:
http://www.devshed.com/c/a/Python/Fi...ent-in-Python/

HTH,
-- Marcel

[Steve Holden]

Re: Basic file operation questions

alex wrote:
[color=blue]
> Hi,
>
> I am a beginner with python and here is my first question:
> How can I read the contents of a file using a loop or something? I open
> the file with file=open(filen ame, 'r') and what to do then? Can I use
> something like
>
> for xxx in file:
> ....
>[/color]
Yes, indeed you can. That's by no means *all* you can do, but to iterate
over the lines of the file that will wrok exactly. Note that the lines
will still have their terminating "\n" on the end, which is why the
print statement inthe following example ends in a comma (this stops
print from putting out its own newline).
[color=blue][color=green][color=darkred]
>>> f = file("test92.py ", 'r')
>>> for l in f:[/color][/color][/color]
... print l,
...
import os.path

def getHomeDir():
''' Try to find user's home directory, otherwise return current
directory.''
'
try:
path1=os.path.e xpanduser("~")
except:
path1=""
try:
path2=os.enviro n["HOME"]
except:
path2=""
try:
path3=os.enviro n["USERPROFIL E"]
except:
path3=""

if not os.path.exists( path1):
if not os.path.exists( path2):
if not os.path.exists( path3):
return os.getcwd()
else: return path3
else: return path2
else: return path1

print getHomeDir()[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

regards
Steve
--
Meet the Python developers and your c.l.py favorites March 23-25
Come to PyCon DC 2005 http://www.python.org/pycon/2005/
Steve Holden http://www.holdenweb.com/

[David Douard]

Re: Basic file operation questions

Marcel van den Dungen wrote:
[color=blue]
> alex wrote:[color=green]
>> Hi,
>>
>> I am a beginner with python and here is my first question:
>> How can I read the contents of a file using a loop or something? I open
>> the file with file=open(filen ame, 'r') and what to do then? Can I use
>> something like
>>
>> for xxx in file:
>> ....
>>
>>
>> Thanks for help
>> Alex
>>[/color]
> take a look at this:
> http://www.devshed.com/c/a/Python/Fi...ent-in-Python/
>
> HTH,
> -- Marcel[/color]

Or even have a look at the excellent Gnosis book on the subject (and very
much more further, but...):
http://gnosis.cx/TPiP/ which is freely available in text format.

David

[David Douard]

Re: Basic file operation questions

David Douard wrote:
[color=blue]
> Marcel van den Dungen wrote:
>[color=green]
>> alex wrote:[color=darkred]
>>> Hi,
>>>
>>> I am a beginner with python and here is my first question:
>>> How can I read the contents of a file using a loop or something? I open
>>> the file with file=open(filen ame, 'r') and what to do then? Can I use
>>> something like
>>>
>>> for xxx in file:
>>> ....
>>>
>>>
>>> Thanks for help
>>> Alex
>>>[/color]
>> take a look at this:
>> http://www.devshed.com/c/a/Python/Fi...ent-in-Python/
>>
>> HTH,
>> -- Marcel[/color]
>
> Or even have a look at the excellent Gnosis book on the subject (and very
> much more further, but...):
> http://gnosis.cx/TPiP/ which is freely available in text format.
>
> David[/color]

Just to tell (it's not clear at all in my message): the author of the book
and creator of Gnosis Software is David Mertz, and the book is published
by Addison Wesley.
Sorry

David

[Caleb Hattingh]

Re: Basic file operation questions

Peter, that was very clear, thanks.
[color=blue]
> So not only is
>
> for line in file(...):
> # do stuff
>
> the most elegant, it is also the fastest. file.readlines( ) comes[/color]
close, but[color=blue]
> is only viable for "small" files.[/color]

[Marc Huffnagle]

Re: Basic file operation questions

When you read a file with that method, is there an implied close() call
on the file? I assume there is, but how is that handled?

Caleb Hattingh wrote:[color=blue]
> Peter, that was very clear, thanks.
>
>[color=green]
>>So not only is
>>
>>for line in file(...):
>> # do stuff
>>
>>the most elegant, it is also the fastest. file.readlines( ) comes[/color]
>
> close, but
>[color=green]
>>is only viable for "small" files.[/color]
>
>[/color]

Marc

[Jeff Shannon]

Re: Basic file operation questions

Marc Huffnagle wrote:
[color=blue]
> When you read a file with that method, is there an implied close() call
> on the file? I assume there is, but how is that handled?
>[/color]
[...][color=blue][color=green][color=darkred]
>>> for line in file(...):
>>> # do stuff[/color][/color][/color]

As I understand it, the disk file will be closed when the file object
is garbage collected. In CPython, that will be as soon as there are
no active references to the file; i.e., in the above case, it should
happen as soon as the for loop finishes. Jython uses Java's garbage
collector, which is a bit less predictable, so the file may not be
closed immediately. It *will*, however, be closed during program
shutdown if it hasn't happened before then.

Jeff Shannon
Technician/Programmer
Credit International

[Caleb Hattingh]

Re: Basic file operation questions

Marc

I don't know how it is handled, but I expect also that there is an implied
close().

thanks
Caleb
[color=blue]
> When you read a file with that method, is there an implied close() call
> on the file? I assume there is, but how is that handled?[/color]

[Grant Edwards]

Re: Basic file operation questions

On 2005-02-08, Marc Huffnagle <mhuffnagle@kno wtechnology.net > wrote:
[color=blue][color=green][color=darkred]
>>>for line in file(...):
>>> # do stuff[/color][/color][/color]
[color=blue]
> When you read a file with that method, is there an implied close() call
> on the file? I assume there is, but how is that handled?[/color]

The file will be closed when the the file object is deleted by
the garbage collection algorithm. That will happen sometime
after the for loop exits and before the program exits. In
normal C-Python I believe it happens immediately after the for
loop exits. However, that behavior is not guaranteed by the
language spec.

--
Grant Edwards grante Yow! Now that I have my
at "APPLE", I comprehend COST
visi.com ACCOUNTING!!