pyqgis - How to access CRS of shapefile in standalone script?

I'm trying to access the CRS of a layer and use this to create a grid. I followed the answer in this post which works great in QGIS but I would like it to work in a standalone script. Here is a snippet:

for fname in glob.glob("C:\Users\moi\Desktop\Test\Grid\\" + "*.shp"):

    extent = QgsVectorLayer( fname, '', 'ogr' ).extent()
    centerx = (extent.xMinimum() + extent.xMaximum()) / 2
    centery = (extent.yMinimum() + extent.yMaximum()) / 2
    width = extent.xMaximum() - extent.xMinimum()

    height = extent.yMaximum() - extent.yMinimum()
    CRS = QgsMapLayer.crs(fname).authid()

    general.runalg("qgis:creategrid", 1000, 1000, width, height, centerx, centery, 1, CRS, None)

Running the above gives me the following error message:

TypeError: QgsMapLayer.crs(): first argument of unbound method must have type 'QgsMapLayer'

Answer

Bleh, answer was simple.

Just had to replace what I originally wrote:

CRS = QgsMapLayer.crs(fname).authid()

With this:

CRS = QgsVectorLayer( fname, '', 'ogr' ).crs().authid()

Works a treat, hope this helps someone!