How to I do this in Python ?

[Ganesh Pal]

Hi Steven ,

Firstly thanks for responding to the question and also guiding me on how to
post the question in the right order ( general to least important order )

Please find the comments >>> inline

On Fri, 16 Aug 2013 11:51:32 +0530, Ganesh Pal wrote:

> My goal is to create various kinds of files like sparse, regular
> ,directories, hard and symlinks etc
> what would be the best way to do achieve this ?

Use your shell, such as bash or csh or equivalent. For simple tasks like
that, it will solve the problem much more simply than Python.

There are three good reasons for doing this in Python:

- "This is only a small part of a larger Python application."

- "I'm doing this to learn how to use Python."

- "I really hate my shell."

But of you just want to get the job done, and don't care what language
you use, use the shell.


Now, having said that, I'm going to assume you have a good reason to use
Python:

>>>  You  have  hit the nail on the head  - The main goal there was to
learn python and avoid using shell commands as much as possible  , I want
to avoid shell and use Python even if its costly.

        Example : I don' want to create sparse files using  dd   command ( #dd
if=/dev/zero of=sparse-file bs=1 count=1 seek=1024k ) If  the same can be
done  fseek .

         But I guess we might have to d


> Case (2) :
>
> Is there a better way to create the files in Python other than using
> sub process module and running dd command as shown below ..
>
> Example :
>
> # creating sparse File
>  sparse_path = os.path.join(path,'sparsefiles')
>      os.makedirs(sparse_path)
>      os.chdir(sparse_path)
>      sparsefiles = "dd if=/dev/zero of=sp1 count=0 bs=1 seek=10G"
>      process_0 = subprocess.Popen(sparsefiles, stdout=subprocess.PIPE,
> stderr=subprocess.PIPE, shell=True)
>
>     # Creating Regular files
>      Regular_path = os.path.join(path,'regularfiles')
>      os.makedirs(Regular_path)
>      os.chdir(Regular_path)
>      regularfiles = " dd if=/dev/urandom of=file1 count=0 bs=1 seek=10"
>      process_1 = subprocess.Popen(regularfiles, stdout=subprocess.PIPE,
> stderr=subprocess.PIPE, shell=True)

What do you mean by "better"? There's probably nothing that will be
faster at rapidly copying bytes from one file to another than dd. But not
with a blocksize of 1 byte at a time. It's more usual to set bs=512 or
bs=1024.

Oh, I see you're not actually writing anything to the file (count=0). In
that case, instead of using dd, you should use touch.

I'm not sure that shell=True is a good idea.

In Python, to create a new empty file, setting its contents to empty if
it already exists:

open("filename", "w").close()


That will open the file, creating it if it doesn't exist, emptying it if
it does, then close it.

To touch a file without emptying it:

open("filename", "a").close()


To make a sparse file, assuming your file system supports it, I believe
you actually have to write at least one byte to the file:

f = open('foo', 'w')
f.seek(10000)
f.write('\0')
f.close()

>>>   Thanks for the suggestion on creating empty files and  they worked
fine . I was today playing with the temp-file  module to create  temporary
files and directories ,
         Iam yet to explore it completely, but in current context , I had a
quick question using temp-file module is its  possible to create empty
 temporary files and save them on disk in the user-defined path ?
         If  " yes "  then can this also be an alternative and does this
have any drawback  ?


On Fri, Aug 16, 2013 at 4:29 PM, Steven D'Aprano <
steve+comp.lang.python at pearwood.info> wrote:

> Hi Ganesh, and welcome!
>
> Unfortunately, you ask your questions in reverse order. The most general
> (and important) question comes last, and the least important first, so
> I'm going to slice-and-dice your post and answer from most general to
> least.
>
>
> On Fri, 16 Aug 2013 11:51:32 +0530, Ganesh Pal wrote:
>
> > My goal is to create various kinds of files like sparse, regular
> > ,directories, hard and symlinks etc
> > what would be the best way to do achieve this ?
>
> Use your shell, such as bash or csh or equivalent. For simple tasks like
> that, it will solve the problem much more simply than Python.
>
> There are three good reasons for doing this in Python:
>
> - "This is only a small part of a larger Python application."
>
> - "I'm doing this to learn how to use Python."
>
> - "I really hate my shell."
>
> But of you just want to get the job done, and don't care what language
> you use, use the shell.
>
>
> Now, having said that, I'm going to assume you have a good reason to use
> Python:
>
>
> > Case (2) :
> >
> > Is there a better way to create the files in Python other than using
> > sub process module and running dd command as shown below ..
> >
> > Example :
> >
> > # creating sparse File
> >  sparse_path = os.path.join(path,'sparsefiles')
> >      os.makedirs(sparse_path)
> >      os.chdir(sparse_path)
> >      sparsefiles = "dd if=/dev/zero of=sp1 count=0 bs=1 seek=10G"
> >      process_0 = subprocess.Popen(sparsefiles, stdout=subprocess.PIPE,
> > stderr=subprocess.PIPE, shell=True)
> >
> >     # Creating Regular files
> >      Regular_path = os.path.join(path,'regularfiles')
> >      os.makedirs(Regular_path)
> >      os.chdir(Regular_path)
> >      regularfiles = " dd if=/dev/urandom of=file1 count=0 bs=1 seek=10"
> >      process_1 = subprocess.Popen(regularfiles, stdout=subprocess.PIPE,
> > stderr=subprocess.PIPE, shell=True)
>
> What do you mean by "better"? There's probably nothing that will be
> faster at rapidly copying bytes from one file to another than dd. But not
> with a blocksize of 1 byte at a time. It's more usual to set bs=512 or
> bs=1024.
>
> Oh, I see you're not actually writing anything to the file (count=0). In
> that case, instead of using dd, you should use touch.
>
> I'm not sure that shell=True is a good idea.
>
> In Python, to create a new empty file, setting its contents to empty if
> it already exists:
>
> open("filename", "w").close()
>
>
> That will open the file, creating it if it doesn't exist, emptying it if
> it does, then close it.
>
> To touch a file without emptying it:
>
> open("filename", "a").close()
>
>
> To make a sparse file, assuming your file system supports it, I believe
> you actually have to write at least one byte to the file:
>
> f = open('foo', 'w')
> f.seek(10000)
> f.write('\0')
> f.close()
>
>
>
> [...]
> > How do I  loop my script to create 100 of files  like sp1 , sp2 ,sp3,..
> > sp100  .. using the same syntax
>
> To generate the various file names, you need to loop over a counter from
> 1 to 100, and stick the count into a string. Use a for-loop and the range
> function:
>
> for i in range(1, 101):
>     filename = "sp" + str(i)
>     open(filename, "a").close()
>
>
> If you are a C programmer, you might prefer this style:
>
>     filename = "sp%d" % i
>
> Or a more object-oriented style:
>
>     filename = "sp{:d}".format(i)
>
>
>
> --
> Steven
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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