12.17.2 Unpacker Objects

Python 2.2

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12.17.2 Unpacker Objects

The Unpacker class offers the following methods:

reset( data): Resets the string buffer with the given data.

get_position( ): Returns the current unpack position in the data buffer.

set_position( position): Sets the data buffer unpack position to position. You should be careful about using get_position() and set_position().

get_buffer( ): Returns the current unpack data buffer as a string.

done( ): Indicates unpack completion. Raises an Error exception if all of the data has not been unpacked.

In addition, every data type that can be packed with a Packer, can be unpacked with an Unpacker. Unpacking methods are of the form unpack_type(), and take no arguments. They return the unpacked object.

unpack_float( ): Unpacks a single-precision floating point number.

unpack_double( ): Unpacks a double-precision floating point number, similarly to unpack_float().

In addition, the following methods unpack strings, bytes, and opaque data:

unpack_fstring( n): Unpacks and returns a fixed length string. n is the number of characters expected. Padding with null bytes to guaranteed 4 byte alignment is assumed.

unpack_fopaque( n): Unpacks and returns a fixed length opaque data stream, similarly to unpack_fstring().

unpack_string( ): Unpacks and returns a variable length string. The length of the string is first unpacked as an unsigned integer, then the string data is unpacked with unpack_fstring().

unpack_opaque( ): Unpacks and returns a variable length opaque data string, similarly to unpack_string().

unpack_bytes( ): Unpacks and returns a variable length byte stream, similarly to unpack_string().

The following methods support unpacking arrays and lists:

unpack_list( unpack_item): Unpacks and returns a list of homogeneous items. The list is unpacked one element at a time by first unpacking an unsigned integer flag. If the flag is 1, then the item is unpacked and appended to the list. A flag of 0 indicates the end of the list. unpack_item is the function that is called to unpack the items.

unpack_farray( n, unpack_item): Unpacks and returns (as a list) a fixed length array of homogeneous items. n is number of list elements to expect in the buffer. As above, unpack_item is the function used to unpack each element.

unpack_array( unpack_item): Unpacks and returns a variable length list of homogeneous items. First, the length of the list is unpacked as an unsigned integer, then each element is unpacked as in unpack_farray() above.

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