def get_darktime(self, img):
        """Obtain DARKTIME"""
        header = self.get_header(img)
        if 'DARKTIME' in header.keys():
            return header['DARKTIME']
        else:
            return self.get_exptime(img)
def get_darktime ( self , img ) : header = self . get_header ( img ) if 'DARKTIME' in header . keys ( ) : return header [ 'DARKTIME' ] else : return self . get_exptime ( img )
Obtain DARKTIME