Preliminary

I need to read a binary file constructed by writing a Struct to it with Python. So I decided to write a simple wrapper using struct module.

Code

import struct


class structure:
    def __init__ ( self, little_endian = True ):
        self._little_endian = little_endian

        self._table  = dict() #stores field name, its format and value 
        self._pack  = list()  #stores field names in order fields must be read


    def add_field( self, field_name, field_format ):
        if field_name in self._table.keys():
            print "WARNING :: Field with name '%s' already exists in this structure" % field_name 
        elif field_format == "":
            print "WARNING :: Format cannot be an empty string"
        else:
            self._table[ field_name ] = { "format" : field_format, "value" : None }
            self._pack.append( field_name )
        #maybe error handling is required here


    def get_value( self, field_name ):
        try:
            return self._table[ field_name ][ "value" ]
        except KeyError:
            print "WARNING :: There is no such field named '%s' in this structure" % field_name 
            return None


    def get_format_string( self ):
        f_str = ""

        for key in self._pack:
            f_str += self._table[ key ][ "format" ]

        if (self._little_endian == True):
            f_str = "<" + f_str
        else:
            f_str = ">" + f_str

        return f_str


    def get_size( self ):
        return struct.calcsize( self.get_format_string() )


    def fill( self, file_ptr ):
        result = struct.Struct( self.get_format_string() ).unpack( file_ptr.read( self.get_size() ) )
        for (i,key) in enumerate(self._pack):
            self._table[ key ][ "value" ] = result[ i ]


    def show( self ):
        print "General info:"
        print "%20s = %s"  % ( "Format string", self.get_format_string() )
        print "%20s = %d" % ( "Size (bytes)", self.get_size() ) 
        print "Value:"
        for key in self._pack:
            print "%20s = " % key, self._table[ key ][ "value" ]

Usage

Usage is straightforward. I used the real binary produced by OWON oscilloscope here so some of the values might look strange (consist non-printable characters).

import structure


s = structure.structure( little_endian=True )
s.add_field( "header", "10s" )
s.add_field( "serial", "14s" )
s.add_field( "string", "18s" )
s.add_field( "trig_time", "f" )
s.add_field( "float1", "f" )
s.add_field( "float2", "f" )

with open( "./data/trigger.bin" ) as f:
    s.fill( f )

s.show()

Output

General info:
       Format string = <10s14s18sfff
        Size (bytes) = 54
Value:
              header =  SPBS01e�
              serial =  SDS60621715234
              string =  
           trig_time =  99.0
              float1 =  3.41239206136e-06
              float2 =  0.001953125

As always any suggestions, ideas and critics are appreciated.