check that files exist powerspectrum

analysis/power_spectrum.py

@@ -1,4 +1,5 @@
 import numpy as np
+import os
 
 kmin = 1e-1
 kmax = 2e0
@@ -286,6 +287,10 @@ if __name__ == "__main__":
     if not args.power_spectrum and not args.cross_correlation:
         print('You must choose between power_spectrum and cross_correlation.')
         exit()
+    
+    for _k,f in enumerate(args.filenames):
+        if not os.path.exists(args.directory+f):
+            raise FileNotFoundError(f"File {args.directory+f} does not exist.")
 
     if args.reference is not None:
         from pysbmy.field import read_field