[Tutor] Writing to a file/changing the file name

[Christian Witts]

On 2012/02/23 07:04 AM, Michael Lewis wrote:
> Hi everyone,
>
> I have a program where I open a file (recipe.txt), I read that file 
> and write it to another file. I am doing some multiplying of numbers 
> in between; however, my question is, when I name the file I am writing 
> to, the file extension is changed, but the file name is not. What am I 
> doing wrong?
>
> Code:
>
> import Homework5_1 as multiply
>
> def MultiplyNumbersInFile(file_name, multiplier):
>     '''Open file/read file/write new file that doubles all int's in the
>     read file'''
>     try:
>         read_file = open(file_name)
>     except IOError:
>         print "I can't find file: ", file_name
>         return
>     new_file_name = file_name + '2'
>     try:
>         write_file = open(new_file_name, 'w')
>     except IOError:
>         read_file.close()
>         print "I can't open file: ", new_file_name
>         return
>     for line in read_file:
>         new_line = line.split()
>         new_line = ''.join(multiply.MultiplyText(new_line, multiplier))
>         write_file.write(new_line + '\n')
>     read_file.close()
>     write_file.close()
>
> def main():
>     file_name = raw_input('What file do you want to open? ')
>     multiplier = multiply.GetUserNumber()
>     MultiplyNumbersInFile(file_name, multiplier)
>
> if __name__ == '__main__':
>     main()
>
> What I am doing in IDLE:
>
> What file do you want to open? recipe.txt
> Enter a multiplier: 2
>
> The file that is actually created in my directory is still named 
> recipe; however, the file type is now TXT2 File. How do I make it so I 
> am updating the file name to recipe2 instead of the file type?
>
>
> -- 
> Michael J. Lewis
>
>
>
> _______________________________________________
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That's because your `file_name` variable contains the file name and 
extension.  You will need to split it into it's component pieces and 
then put it back together once you've changed the name, and for that you 
can use os.path.splitext

 >>> import os
 >>> filename, extension = os.path.splitext('recipe.txt')
 >>> print (filename, extension)
('recipe', '.txt')
 >>> new_filename = filename + '2' + extension
 >>> print new_filename
'recipe2.txt'

-- 

Christian Witts
Python Developer
//
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