<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_content_hash(self):
 """ Compute and return the MD5 hash for this file. """

        if not self.rexists():
            return SCons.Util.MD5signature('')
        fname = self.rfile().get_abspath()
        try:
            cs = SCons.Util.MD5filesignature(fname,
                chunksize=SCons.Node.FS.File.md5_chunksize*1024)
        except EnvironmentError as e:
            if not e.filename:
                e.filename = fname
            raise
        return cs