Save created file into new directory in loop

Question

I am currently updating some files I have in a directory, with a loop, and I would like to save those file in a different directory.

Here is what I have:

from astropy.io import fits
from mpdaf.obj import Spectrum, WaveCoord
import os, glob

ROOT_DIR=input("Enter root directory : ")
os.chdir(ROOT_DIR)
destination=input("Enter destination directory : ")

fits_files = glob.glob("*.fits")

for spect in fits_files:
    spe = Spectrum(filename= spect, ext=[0,1])
    (spect_name, ext) = os.path.splitext(spect)
    sperebin = spe.rebin(57)
    sperebin.write(spect_name + "-" + "rebin" + ".fits")

With the last line sperebin.write(spect_name + "-" + "rebin" + ".fits") it is currently writing the file in the directory I'm in, and I would like it to write it directly into the destination directory, any idea how to proceed?

Answer 1

You don't need to or want to change directories in your script. Instead, use pathlib to simplify the creation of the new filename.

from pathlib import Path

root_dir = Path(input("Enter root directory : "))
destination_dir = Path(input("Enter destination directory : "))

# Spectrum wants a string for the filename argument
# so you need to call str on the Path object
for pth in root_dir.glob("*.fits"):
    spe = Spectrum(filename=str(pth), ext=[0,1])
    sperebin = spe.rebin(57)
    dest_pth = destination_dir / pth.stem / "-rebin" / pth.suffix
    sperebin.write(str(dest_pth))

Answer 2

With os.path.join you can combine directory with filename to get the file path.

sperebin.write(os.path.join(destination, pect_name + "-" + "rebin" + ".fits"))

Also with os you can check if the directory exists and create it if you want to.

if not os.path.exists(destination):
    os.makedirs(destination)