You might want to use the Clip_management tool (clips rasters w/ option to use a polygons). Note this is different from the Clip_analysis tool which is for vectors.
If your charts are in a color mapped multiband image format (.tif, .jpg, etc), you will find that the the Clip_management tool is much easier to deal with.
Also, be sure to use the "gp.snapraster" environment setting to ensure that the output rasters have the same cell alignment as the input rasters.
So it might look something like this:
import sys, string, os, arcgisscripting
gp = arcgisscripting.create()
try:
gp.CheckOutExtension("spatial")
gp.AddToolbox("C:/Arquivos de programas/ArcGIS/ArcToolbox/Toolboxes/Spatial Analyst Tools.tbx")
gp.workspace = "E:/GIS_Mestrado/Corumbatai/3_Cartas_um_metro"
out_workspace = "E:/GIS_Mestrado/Corumbatai/4_Cartas_Con/"
mascara = "E:/GIS_Mestrado/Corumbatai/Geodados/Grid_Cartas_sem_Grade.shp"
rasters = gp.ListRasters()
raster = rasters.next()
while raster:
gp.extent = gp.describe(raster).extent
gp.snapraster = raster
output = out_workspace + raster + ".tif" #reformat as a .tif or whatever - it's that easy!
gp.Clip_management(raster, gp.extent, output, mascara, "", "CLIPPINGGEOMETRY")
gp.extent = "" #clear the extent
raster = rasters.next()
except:
print "Error in script"
print gp.GetMessages().