Python equivalent of gdalbuildvrt

The answer of @rcoup only worked for me, if modify it as follows:

from osgeo import gdal 

vrt_options = gdal.BuildVRTOptions(resampleAlg='cubic', addAlpha=True)
my_vrt = gdal.BuildVRT('my.vrt', ['one.tif', 'two.tif'], options=vrt_options)
my_vrt = None

Otherwise, the file is not written to disk.

Honestly it's easier to do this by using gdalbuildvrt in a subprocess or os.system.

Should you wish to do this through Python it can be done. Using the standard dataset creation methods within GDAL Python we can easily create the base dataset VRT.

from osgeo import gdal

drv = gdal.GetDriverByName("VRT")
vrt = drv.Create("test.vrt", x_size, y_size, 0)

Note that we are creating the dataset with no bands initially. From the documentation on VRTs that VRT datasets are one of the few dataset types that can accept AddBand arguments.

vrt.AddBand(gdal.GDT_Float32)
band = vrt.GetRasterBand(1)

Now for each band we have to set the metadata items manually:

simple_source = '<SourceFilename relativeToVRT="1">%s</SourceFilename>' % source_path + \
    '<SourceBand>%i</SourceBand>' % source_band + \
    '<SourceProperties RasterXSize="%i" RasterYSize="%i" DataType="Real" BlockXSize="%i" BlockYSize="%i"/>' % (x_size, y_size, x_block, y_block) + \
    '<SrcRect xOff="%i" yOff="%i" xSize="%i" ySize="%i"/>' % (x_offset, y_offset, x_source_size, y_source_size) + \
    '<DstRect xOff="%i" yOff="%i" xSize="%i" ySize="%i"/>' % (dest_x_offset, dest_y_offset, x_dest_size, y_dest_size)
band.SetMetadataItem("SimpleSource", simple_source)
band.SetMetadataItem("NoDataValue", -9999)

SetMetadatItem takes two arguments, the first a string of the metadata item, the second the item itself. This means that you can't subset a metadata item, so for data sources you have to set the entire contents as a string.

Note that we can use this method to create complex sources (ComplexSource) that contain look-up-tables of values, Kernel filter sources (KernelFilteredSource) of arbitrary sizes and shapes, and Mask Bands (MaskBand).

Since GDAL 2.1 the CLI tools are available as library functions, and in fact that's what the CLI tools now call internally.

For example:

gdalbuildvrt -r cubic -addalpha my.vrt one.tif two.tif

Is the equivalent of:

from osgeo import gdal

vrt_options = gdal.BuildVRTOptions(resampleAlg='cubic', addAlpha=True)
gdal.BuildVRT('my.vrt', ['one.tif', 'two.tif'], options=vrt_options)

The available CLI options directly map to the parameters of BuildVRTOptions, plus there's some extras like progress callbacks available.