Wand : no decode delegate for this image format `'

Question

I'm using Wand in order to convert the first page from PDF files into jpg files and than, apply some processes with another script.

My problem is : Since yesterday, I obtain this error and I don't get any solution. I tried to re-install imagemagick but none effects.

This is the Traceback message :

Traceback (most recent call last):
  File "conversion.py", line 9, in <module>
    convert = Image(filename="/Users/valentinjungbluth/Desktop/NAPS_PDF/" + PDF)  
  File "/usr/local/lib/python2.7/site-packages/wand/image.py", line 2744, in __init__
    self.read(filename=filename, resolution=resolution)
  File "/usr/local/lib/python2.7/site-packages/wand/image.py", line 2822, in read
    self.raise_exception()
  File "/usr/local/lib/python2.7/site-packages/wand/resource.py", line 222, in raise_exception
    raise e
wand.exceptions.MissingDelegateError: no decode delegate for this image format `' @ error/constitute.c/ReadImage/504
Exception TypeError: TypeError("object of type 'NoneType' has no len()",) in <bound method Image.__del__ of <wand.image.Image: (empty)>> ignored

Do you have some idea about this problem ?

This is my script which let to convert PDF to JPG :

#-*- coding: utf-8 -*-

from wand.image import Image
import os


for PDF in os.listdir ("/Users/valentinjungbluth/Desktop/NAPS_PDF/") : #boucle sur tous les PDF du dossier

        convert = Image(filename="/Users/valentinjungbluth/Desktop/NAPS_PDF/" + PDF)  
        name = PDF.split('.') #Récupération du nom
        page = len(convert.sequence)

        if page == 1 :  #Nombre de page = 1
                convert.compression_quality = 100 #Qualité en %
                convert.save(filename="/Users/valentinjungbluth/Desktop/PDF_to_JPG/" + name[0] + ".jpg") #Enregistrement en JPEG sous la forme nom.jpg

        elif page > 1 : #Nombre de page > 1

                for frame in convert.sequence : #Pour chaque page 
                        img_page = Image(image=frame)
                        img_page.compression_quality = 100 #Qualité en %
                        img_page.save(filename="/Users/valentinjungbluth/Desktop/PDF_to_JPG/" + name[0] + ".jpg") #Enregistrement en JPEG sous la forme nom.jpg
                        break

Thank you so much

EDIT :

It works with this simple script :

#-*- coding: utf-8 -*-

from wand.image import Image
import os

with Image(filename="/Users/valentinjungbluth/Desktop/NAPS_PDF/arrow.pdf", resolution=200) as convert : 

        convert.compression_quality = 150 #Qualité en %
        convert.save(filename="/Users/valentinjungbluth/Desktop/PDF_to_JPG/test.jpg") #Enregistrement en JPEG sous la forme nom.jpg

SOLUTION :

On MacOSX, I have a file which is named : .DS_Store I have to delete it or just take .pdf files ! My error came from this .DS_Store file !