import os
import ogr
from osgeo import gdal

def getRasterBox(raster):
    src = gdal.Open(raster)
    ulx, xres, xskew, uly, yskew, yres = src.GetGeoTransform()
    lrx = ulx + (src.RasterXSize * xres)
    lry = uly + (src.RasterYSize * yres)
    return (uls, uly, lrx, lry)

def findUTMzone(raster_box, utmgrid):
    # do the stuff

utmzone_path = r'C:temp'
utmzone_file = 'utm_grid.shp'
utmzone = os.path.join(utmzone_path, utmzone_file)

utm_ds = ogr.Open(utmzone)
utm_layer = utm_ds.GetLayer()

rasterdir = r'C:temp'
raster_file = 'n38.tif'
raster = os.path.join(rasterdir, raster_file)

rasterdetails = getRasterBox(raster)
rasterWKT = 'POLYGON(({} {}, {} {}, {} {}, {} {}, {} {}))'.format(rasterdetails[0], rasterdetails[1], rasterdetails[0], rasterdetails[3], rasterdetails[2], rasterdetails[3], rasterdetails[2], rasterdetails[1], rasterdetails[0], rasterdetails[1])