Output layer doesn't get created [closed]

Question

Why isn't my heat layer valid and I don't get a .tif in this location (this location exists 100%)? Code below:

output = "D:/QGIS_Project_New/heat_map_last.tif"
heat = QgsRasterLayer(output, "Heatmap")
QgsMapLayerRegistry.instance().addMapLayers([heat])
if heat.isValid() is True:
print "Layer was loaded successfully!"
else:
print "Unable to read basename and file path - Your string is invalid"

I get the "Unable.." print, why is that?

EDIT:

So my code for loading layers is working:

highway_layer = QgsVectorLayer("D:/Tomas/QGIS_Project_New/points_highway.shp","Highway","ogr")

if highway_layer.isValid() is True:
    print " HIGHWAY Layer was loaded successfully!"
else:
    print " HIGHWAY Unable to read basename and file path - Your string is invalid"

But when I try to create and save a layer on this location it is not working. Also I'm using Python Console in QGIS.