title: Creating a new file with input file name
body: <p>I have a question. How can I rename the output file using the input filename?</p>
  
  <p>For example, my input filename is: </p>
  
  <pre><code>Field_52_combined_final_roughcal.fits
  </code></pre>
  
  <p>I would like to obtain an output filename like: </p>
  
  <pre><code>Field_52_traitement_1.fits
  </code></pre>
  
  <p>I know that I could write : </p>
  
  <pre><code>hdu.writeto('Field_52_traitement_1.fits')   
  </code></pre>
  
  <p>But, I have an other script which loop on 200 files, and I would like the output filename being automatically generated by the input filename.</p>
  
  <p>My script looks like this (for a single input file):</p>
  
  <pre><code>#!/usr/bin/python
  # coding: utf-8
  
  from astropy.io import fits
  from astropy.table import Table
  import numpy as np
  
                  ###################################
                  # Fichier contenant le champ brut #
                  ###################################
  
  filename = 'E:/Fields/Field52_combined_final_roughcal.fits'
  
  # Ouverture du fichier à l'aide d'astropy  
  field = fits.open(filename)          
  
  # Lecture des données fits
  tbdata = field[1].data               
  
                  #######################################################
                  # Application du tri en fonction de divers paramètres #
                  #######################################################
  
  Several conditions / sort
  
          ###################################################
          # Ecriture du résultat dans nouveau fichier .fits #
          ###################################################
  
  hdu = fits.BinTableHDU(data=tbdata_final)
  hdu.writeto('{}_{}'.format(filename,'traitement_1'))    
  </code></pre>
  
  <p>But, with this kind of script, I get:</p>
  
  <pre><code>Field_52_combined_final_roughcal.fits_traitement_1
  </code></pre>
  
  <p>Tell me, if you have any ideas, websites or something else :)
  Thank you for your answers!</p>