Cropping pages of a .pdf file

pyPdf does what I expect in this area. Using the following script:

#!/usr/bin/python
#

from pyPdf import PdfFileWriter, PdfFileReader

with open("in.pdf", "rb") as in_f:
    input1 = PdfFileReader(in_f)
    output = PdfFileWriter()

    numPages = input1.getNumPages()
    print "document has %s pages." % numPages

    for i in range(numPages):
        page = input1.getPage(i)
        print page.mediaBox.getUpperRight_x(), page.mediaBox.getUpperRight_y()
        page.trimBox.lowerLeft = (25, 25)
        page.trimBox.upperRight = (225, 225)
        page.cropBox.lowerLeft = (50, 50)
        page.cropBox.upperRight = (200, 200)
        output.addPage(page)

    with open("out.pdf", "wb") as out_f:
        output.write(out_f)

The resulting document has a trim box that is 200×200 points and starts at 25,25 points inside the media box.
The crop box is 25 points inside the trim box.

Here is how my sample document looks in acrobat professional after processing with the above code:

This document will appear blank when loaded in acrobat reader.