How to use the pisa.elf.elf_reader function in pisa

import sys
import os
sys.path.append('/Users/dmlockhart/vc/git-brg/parc/pymtl')
import pisa.elf           as elf
import pisa.pisa_encoding as pisa_encoding

# Load the elf file

source_elf  = sys.argv[1]
path, file_ = os.path.split( source_elf )
dest_elf    = file_+'-new'
mem_image   = None

with open(source_elf,'rb') as file_obj:
  mem_image = elf.elf_reader( file_obj )

# Add a bootstrap section at address 0x400

bootstrap_asm = """
  lui r29, 0x0007
  ori r29, r0, 0xfffc
  j   0x1000
"""

bootstrap_mem_image = pisa_encoding.assemble( bootstrap_asm )
bootstrap_bytes = bootstrap_mem_image.get_section(".text").data
mem_image.add_section( ".bootstrap", 0x400, bootstrap_bytes )

import struct
print len( bootstrap_bytes  )
for i in [0, 4, 8]: