[Tutor] understanding fileinput

[Michael Lange]

On Wed, 07 Apr 2004 22:12:13 +0200
Michele Alzetta <michele.alzetta at aliceposta.it> wrote:

Hi Michele,

> #!/usr/bin/python
> import os, sys, re, fileinput
> 
> try:
>     target_folder = (sys.argv[1])
>     original_pattern = (sys.argv[2])
>     result_pattern = (sys.argv[3])
> except:
>     print "\n Substitutes a string with another in all files of a
> specified directory and its subdirectories"
>     print "Use: ./MyScript.py directory string other_string"
>     sys.exit()
> for folders, folder, filelist in os.walk(target_folder):
>     for filename in filelist:
>         file = os.path.join(folders,filename)
>         for line in fileinput.input(file,'inplace=1'):
>             line = re.sub(original_pattern,result_pattern,line)
>             print line   
> #        fileinput.close()
> 
> I haven't yet tried to add the code for changing filenames but it seems
> pretty straightforward: re.sub + os.rename, I suppose.
> 
> Two questions here:
> 
> - this correctly changes the pattern in filecontent but for some reason
> adds a newline for every newline originally present in the file at every
> pass - why ?
> 

I guess "print line" adds the newline; try "sys.stdout.write(line)" instead.


> - from documentation of fileinput I thought fileinput.close() was
> necessary, but actually commenting it out doesn't change anything for
> good or ill in the working of the program.
> 

fileinput.input() closes the file itself when the end is reached;
You can use the close() method to stop iterating over the file ( and start iterating over the
next file if you pass a tuple of several files to input() ). This might be useful
if you look for a certain pattern in large files to speed up the whole thing I think.

(by the way: be careful using "file" as a variable name, it's a built in function)


> -- 
> Michele Alzetta <michele.alzetta at aliceposta.it>
> 

I hope this helps

Michael