12.9.1 Packer Objects
Keywords: lib

##
12.9.1 Packer Objects

`Packer` instances have the following methods:

`get_buffer` ()
  Returns the current pack buffer as a string.

`reset` ()
  Resets the pack buffer to the empty string.

In general, you can pack any of the most common XDR data types by calling the appropriate `pack_type()` method. Each method takes a single argument, the value to pack. The following simple data type packing methods are supported: `pack_uint()`, `pack_int()`, `pack_enum()`, `pack_bool()`, `pack_uhyper()`, and `pack_hyper()`.

`pack_float` (value)
  Packs the single-precision floating point number value.

`pack_double` (value)
  Packs the double-precision floating point number value.

The following methods support packing strings, bytes, and opaque data:

`pack_fstring` (n, s)
  Packs a fixed length string, s. n is the length of the string but it is not packed into the data buffer. The string is padded with null bytes if necessary to guaranteed 4 byte alignment.

`pack_fopaque` (n, data)
  Packs a fixed length opaque data stream, similarly to `pack_fstring()`.

`pack_string` (s)
  Packs a variable length string, s. The length of the string is first packed as an unsigned integer, then the string data is packed with `pack_fstring()`.

`pack_opaque` (data)
  Packs a variable length opaque data string, similarly to `pack_string()`.

`pack_bytes` (bytes)
  Packs a variable length byte stream, similarly to `pack_string()`.

The following methods support packing arrays and lists:

`pack_list` (list, pack_item)
  Packs a list of homogeneous items. This method is useful for lists with an indeterminate size; i.e. the size is not available until the entire list has been walked. For each item in the list, an unsigned integer `1` is packed first, followed by the data value from the list. pack_item is the function that is called to pack the individual item. At the end of the list, an unsigned integer `0` is packed.

  For example, to pack a list of integers, the code might appear like this:

        import xdrlib
        p = xdrlib.Packer()
        p.pack_list([1, 2, 3], p.pack_int)

`pack_farray` (n, array, pack_item)
  Packs a fixed length list (array) of homogeneous items. n is the length of the list; it is not packed into the buffer, but a `ValueError` exception is raised if `len(array)` is not equal to n. As above, pack_item is the function used to pack each element.

`pack_array` (list, pack_item)
  Packs a variable length list of homogeneous items. First, the length of the list is packed as an unsigned integer, then each element is packed as in `pack_farray()` above.