Obviously the code below will returned null because there's no picture in landsat 8 will contain such a large area.
#python geometry = ee.Geometry.Polygon( [[73.0, 25.0], [73.0, 49.0], [125.0, 25.0], [125.0,49.0]]) landsat = ee.ImageCollection('LANDSAT/LC08/C01/T1_TOA').filterDate(date_start, data_end).filterBounds(geometry)
But I wonder is there any way that can get a Collection contains pictures which can cover the whole area. I'd prefer these pictures are all metadata before mosaic. Mosaic() make no sense because I want to do some pre-process on single picture.