==========================================================
Package Shipment and Address Verification with ``PyDicia``
==========================================================

New in 0.1a3
  * Added ``FlatRateLargeBox`` and ``ExpressMailPremiumService`` tags, for use
    with DAZzle 8.0 and up.

New in 0.1a2
  * Dropped MS Windows requirement; you can now use PyDicia to generate XML for
    the Endicia Mac client, or to be sent via download or networked directory
    to a Windows client.  

  * Added a ``Shipment.run()`` method to allow running multiple batches in
    sequence.

  * Fixed the ``Status.ToZip4`` attribute (it was incorrectly spelled
    ``ToZIP4``, and thus didn't work).
   
PyDicia is a Python interface to endicia.com's postal services client, DAZzle.
Using DAZzle's XML interface, PyDicia can be used to print shipping labels,
envelopes, postcards and more, with or without prepaid US postage indicia
(electronic stamps), as well as doing address verification.

In addition to providing a layer of syntax sugar for the DAZzle XML interface,
PyDicia provides a novel adaptive interface that lets you smoothly integrate
its functions with your application's core types (like invoice, customer, or
"packing slip" objects) without subclassing.  (This is particularly useful if
you are extending a CRM or other database that was written by somebody else.)

This version of PyDicia is an alpha proof-of-concept release.  It is actually
usable -- I've in fact been using it in production for over a year, shipping
dozens of envelopes and packages a month all over the US, Canada, and Europe.
However, the API is still potentially subject to change, the reference
documentation is sketchy, and the developer's guide lacks detail about some of
the more advanced features.  This should improve in future releases, but at
least this way, you can use it now, if you need something like it.  Reading the
`DAZzle XML API specification`_ is a good idea if you want to use this, though;
the 8.0 version is the latest, although PyDicia also supports 7.0.x versions.

.. _DAZzle XML API specification: http://fileserver.surveygizmo.com/users/4508/dazzleXMLInterfaceV8.pdf

PyDicia uses the ElementTree, simplegeneric, and DecoratorTools packages, and
requires Python 2.4 or higher (due to use of decorators and the ``Decimal``
type).  Actually printing any labels requires that you have an Endicia
"Premium" or "Mac" account.  (Note: I have not used the Mac client, so I don't
know how well it works there.  See the section below on `Using PyDicia on
Non-Windows Platforms`_ for more info.)

IMPORTANT
    Please note that PyDicia does not attempt to implement all of the US Postal
    Service's business rules for what options may be used in what combinations.
    It doesn't even validate most of the DAZzle client's documented
    restrictions!  So it's strictly a "Garbage In, Garbage Out" kind of deal.
    If you put garbage in, who knows what the heck will happen.  You might end
    up spending lots of money *and* getting your packages returned to you --
    and **I AM NOT RESPONSIBLE**, even if your problem is due to an error in
    PyDicia or its documentation!

    So, make sure you understand the shipping options you wish to use, and test
    your application thoroughly before using this code in production.  You have
    been warned!

Questions, discussion, and bug reports for this software should be directed to
the PEAK mailing list; see http://www.eby-sarna.com/mailman/listinfo/PEAK/
for details.

.. contents:: **Table of Contents**


-----------------
Developer's Guide
-----------------


Basic XML Generation
====================

PyDicia simplifies the creation of XML for DAZzle by using objects to specify
what data needs to go in the XML.  These objects are mostly ``Option``
instances, or callables that create ``Option`` instances.  However, the
framework is extensible, so that you can use your own object types with the
same API.  Your object types can either generate ``Option`` instances, or
directly manipulate the XML using ElementTree APIs for maximum control.

In the simpler cases, however, you will just use lists or tuples of objects
provided by (or created with) the PyDicia API to represent packages or labels.


Batch Objects
-------------

XML documents are represented using ``Batch`` objects::

    >>> from pydicia import *
    >>> b = Batch()

The ``tostring()`` method of a batch returns its XML in string form, optionally
in a given encoding (defaulting to ASCII if not specified)::

    >>> print b.tostring('latin1')
    <?xml version='1.0' encoding='latin1'?>
    <DAZzle />

To add a package to a batch, you use the ``add_package()`` method::

    >>> b.add_package(ToName('Phillip Eby'))
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
             <ToName>Phillip Eby</ToName>
        </Package>
    </DAZzle>

The ``add_package()`` method accepts zero or more objects that can manipulate
PyDicia package objects.  It also accepts tuples or lists of such objects,
nested to arbitrary depth::

    >>> b.add_package([Services.COD, (Stealth, ToName('Ty Sarna'))], FlatRateBox)

    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <ToName>Phillip Eby</ToName>
        </Package>
        <Package ID="2">
            <Services COD="ON" />
            <Stealth>TRUE</Stealth>
            <ToName>Ty Sarna</ToName>
            <PackageType>FLATRATEBOX</PackageType>
        </Package>
    </DAZzle>

And the ``packages`` attribute of a batch keeps track of the arguments that
have been passed to ``add_package()``::

    >>> b.packages
    [Package(ToName('Phillip Eby'),),
     Package([Services.COD('ON'), (Stealth('TRUE'), ToName('Ty Sarna'))],
      PackageType('FLATRATEBOX'))]

Each package object in the list wraps a tuple of the arguments that were
supplied for each invocation of ``add_package()``.  This allows the system
to send status updates (including delivery confirmation numbers, customs IDs,
etc.) back to the application.

But before we can process status updates, we need to have some application
objects, as described in the next section.


Using Your Application Objects as Package Sources
-------------------------------------------------

In addition to PyDicia-defined objects and sequences thereof, the
``add_package()`` method also accepts any custom objects of your own design
that have been registered with the ``pydicia.add_to_package()`` or
``pydicia.iter_options()`` generic functions::

    >>> class Customer:
    ...     def __init__(self, **kw):
    ...         self.__dict__ = kw

    >>> @iter_options.when_type(Customer)
    ... def cust_options(ob):
    ...     yield ToName(ob.name)
    ...     yield ToAddress(ob.address)
    ...     yield ToCity(ob.city)
    ...     yield ToState(ob.state)
    ...     yield ToPostalCode(ob.zip)

    >>> b = Batch()
    >>> c = Customer(
    ...     name='PJE', address='123 Nowhere Dr', state='FL', city='Nowhere',
    ...     zip='12345-6789'
    ... )
    >>> b.add_package(c)
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <ToName>PJE</ToName>
            <ToAddress1>123 Nowhere Dr</ToAddress1>
            <ToCity>Nowhere</ToCity>
            <ToState>FL</ToState>
            <ToPostalCode>12345-6789</ToPostalCode>
        </Package>
    </DAZzle>

This allows you to pass customer, package, product, invoice, or other
application-specific objects into ``add_package()``.  And the objects yielded
by your ``iter_options`` implementation can also be application objects, e.g.::

    >>> class Invoice:
    ...     def __init__(self, **kw):
    ...         self.__dict__ = kw

    >>> @iter_options.when_type(Invoice)
    ... def invoice_options(ob):
    ...     yield ob.shippingtype
    ...     yield ob.products
    ...     yield ob.customer

    >>> b = Batch()
    >>> i = Invoice(
    ...     shippingtype=(Tomorrow, MailClass('MEDIAMAIL')),
    ...     products=[WeightOz(27),], customer=c
    ... )
    >>> b.add_package(i)
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <DateAdvance>1</DateAdvance>
            <MailClass>MEDIAMAIL</MailClass>
            <WeightOz>27</WeightOz>
            <ToName>PJE</ToName>
            <ToAddress1>123 Nowhere Dr</ToAddress1>
            <ToCity>Nowhere</ToCity>
            <ToState>FL</ToState>
            <ToPostalCode>12345-6789</ToPostalCode>
        </Package>
    </DAZzle>

Note that there is no particular significance to my choice of lists vs. tuples
in these examples; they're more to demonstrate that you can use arbitrary
structures, as long as they contain objects that are supported by either
``iter_options()`` or ``add_to_package()``.  Normally, you will simply use
collections of either PyDicia-provided symbols, or application objects for
which you've defined an ``iter_options()`` method.

You will also usually want to implement your PyDicia support in a module by
itself, so you can use ``from pydicia import *`` without worrying about symbol
collisions.


Batch-wide Options
------------------

When you create a batch, you can pass in any number of objects, to specify
options that will be applied to every package.  For example, this batch will
have every package set to be mailed tomorrow as media mail::

    >>> b = Batch( Tomorrow, MailClass('MEDIAMAIL') )
    >>> b.add_package(ToName('PJE'))
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <ToName>PJE</ToName>
            <DateAdvance>1</DateAdvance>
            <MailClass>MEDIAMAIL</MailClass>
        </Package>
    </DAZzle>


Multi-Batch Shipments
=====================

Certain DAZzle options can only be set once per XML file, such as the choice of
layout file.  If you are shipping multiple packages with different label
layouts (such as domestic vs. international mail), you need to separate these
packages into different batches, each of which will be in a separate XML file.
The ``Shipment`` class handles this separation for you automatically.

When you create a shipment, it initially has no batches::

    >>> s = Shipment()
    >>> s.batches
    []


But as you add packages to it, it will create batches as needed::

    >>> s.add_package(ToName('Phillip Eby'), DAZzle.Test)
    >>> len(s.batches)
    1

    >>> print s.batches[0].tostring()
    <DAZzle Test="YES">
        <Package ID="1">
            <ToName>Phillip Eby</ToName>
        </Package>
    </DAZzle>

As long as you're adding packages with the same or compatible options, the
same batch will be reused::

    >>> s.add_package(ToName('Ty Sarna'), DAZzle.Test)
    >>> len(s.batches)
    1
    >>> print s.batches[0].tostring()
    <DAZzle Test="YES">
        <Package ID="1">
            <ToName>Phillip Eby</ToName>
        </Package>
        <Package ID="2">
            <ToName>Ty Sarna</ToName>
        </Package>
    </DAZzle>

But as soon as you add a package with any incompatible options, a new batch
will be created and used::

    >>> s.add_package(ToName('PJE'), ~DAZzle.Test)
    >>> len(s.batches)
    2

    >>> print s.batches[1].tostring()
    <DAZzle Test="NO">
        <Package ID="1">
            <ToName>PJE</ToName>
        </Package>
    </DAZzle>

And each time you add a package, it's added to the first compatible batch::

    >>> s.add_package(ToName('Some Body'), ~DAZzle.Test)
    >>> len(s.batches)
    2

    >>> print s.batches[1].tostring()
    <DAZzle Test="NO">
        <Package ID="1">
            <ToName>PJE</ToName>
        </Package>
        <Package ID="2">
            <ToName>Some Body</ToName>
        </Package>
    </DAZzle>

    >>> s.add_package(ToName('No Body'), DAZzle.Test)
    >>> len(s.batches)
    2

    >>> print s.batches[0].tostring()
    <DAZzle Test="YES">
        <Package ID="1">
            <ToName>Phillip Eby</ToName>
        </Package>
        <Package ID="2">
            <ToName>Ty Sarna</ToName>
        </Package>
        <Package ID="3">
            <ToName>No Body</ToName>
        </Package>
    </DAZzle>

By the way, as with batches, you can create a shipment with options that will
be applied to all packages::

    >>> s = Shipment(Tomorrow, Services.COD)
    >>> s.add_package(ToName('Some Body'), DAZzle.Test)
    >>> s.add_package(ToName('No Body'), ~DAZzle.Test)
    >>> len(s.batches)
    2
    >>> print s.batches[0].tostring()
    <DAZzle Test="YES">
        <Package ID="1">
            <ToName>Some Body</ToName>
            <DateAdvance>1</DateAdvance>
            <Services COD="ON" />
        </Package>
    </DAZzle>

    >>> print s.batches[1].tostring()
    <DAZzle Test="NO">
        <Package ID="1">
            <ToName>No Body</ToName>
            <DateAdvance>1</DateAdvance>
            <Services COD="ON" />
        </Package>
    </DAZzle>



Receiving Status Updates
========================

When DAZzle completes a batch, it creates an output file containing status
information for each package in the batch.  If you'd like to process this
status information for the corresponding application objects you passed in
to ``add_package()``, you can extend the ``report_status()`` generic function
to do this::

    >>> @report_status.when_type(Customer)
    ... def customer_status(ob, status):
    ...     print ob
    ...     print status

    >>> b = Batch()
    >>> b.add_package(c)

When the batch receives status information, it will invoke ``report_status()``
on each package's application items, with a status object for the corresponding
package::

    >>> b.report_statuses()
    <...Customer instance...>
    ToAddress           : [u'123 Nowhere Dr']
    ToCity              : u'Nowhere'
    ToState             : u'FL'
    ToPostalCode        : u'12345-6789'
    ToAddress1          : u'123 Nowhere Dr'

Note that you don't normally need to call ``report_statuses()`` directly; it's
usually done for you as part of the process of running a batch or shipment.
(See the section below on `Invoking DAZzle`_.)

The `status` object passed to your method will be a ``Status`` instance with
attributes similar to those above, containing USPS-normalized address data.
In addition, several other fields are possible::

    >>> from pydicia import ET
    >>> b.etree = ET.fromstring('''
    ... <DAZzle><Package ID="1">
    ...     <ToZip4>1234</ToZip4>
    ...     <Status>Rejected (-3)</Status>
    ...     <PIC>123465874359</PIC>
    ...     <FinalPostage>4.60</FinalPostage>
    ...     <TransactionDateTime>20070704173221</TransactionDateTime>
    ...     <PostmarkDate>20070705</PostmarkDate>
    ... </Package></DAZzle>''')

    >>> b.report_statuses()
    <...Customer instance...>
    Status              : 'Rejected (-3)'
    ErrorCode           : -3
    ToAddress           : []
    ToZip4              : '1234'
    PIC                 : '123465874359'
    FinalPostage        : Decimal("4.60")
    TransactionDateTime : datetime.datetime(2007, 7, 4, 17, 32, 21)
    PostmarkDate        : datetime.date(2007, 7, 5)

The ``Status`` object should support all output fields supported by DAZzle; see
the DAZzle documentation for details.  The non-string fields shown above are
the only ones which are postprocessed to specialized Python objects; the rest
are kept as strings or Unicode values.  The ``ErrorCode`` field is computed by
extracting the integer portion of any rejection code.  It is ``None`` in the
case of a successful live print, and ``0`` in the case of a successful test
print.  See the DAZzle XML interface documentation for a description of other
error codes.

Note that for a more compact presentation, attributes with ``None`` values are
not included in the ``str()`` of a ``Status`` object, which is why the statuses
displayed above show different sets of fields.  The attributes, however, always
exist; they simply have ``None`` as their value.


Invoking DAZzle
===============

In the simplest case, invoking a batch or shipment object's ``.run()`` method
will launch a local copy of DAZzle on a temporary file containing the batch's
XML, wait for DAZzle to exit, then process status updates from the output file
and return DAZzle's return code.  (Or a list of return codes, in the case of a
``Shipment``.)

If you are using this approach, you may wish to include ``~DAZzle.Prompt``
(which keeps end-user prompts to a minimum) and ``DAZzle.AutoClose`` (so that
DAZzle exits upon completion of the batch) in your batch options.

If you do not have a local copy of DAZzle, but instead are using a network
queue directory to send jobs remotely, you can instead use the batch object's
``.write(queuedir)`` method to send the batch to the queue.  You can also
use this approach to send jobs to a local copy of DAZzle running in the
background.

If a copy of DAZzle is installed locally, you can get its XML queue directory
from ``DAZzle.XMLDirectory``, and check whether it is monitoring for files
using ``DAZzle.get_preference("MonitorXML")``.  (These values will be ``None``
if DAZzle is not installed.)

If DAZzle is installed locally, you can launch it with the
``DAZzle.run(args=(), sync=True)`` function.  The `args` are a list of command
line arguments to pass, and `sync` is a flag indicating whether to wait for
DAZzle to exit.  If `sync` is a false value, ``run()`` returns a
``subprocess.Popen`` instance.  Otherwise, it returns the process's exit code
(ala ``subprocess.call``).

XXX async batch status retrieval

XXX DAZzle.exe_path, DAZzle.get_preference(), DAZzle.LayoutDirectory

XXX Launching for multi-batch, remote, queued, and other async processing


Using PyDicia on Non-Windows Platforms
======================================

When used on a non-Windows platform, PyDicia cannot detect any DAZzle
configuration information, so you must manually set ``DAZzle.exe_path`` to
the client program, if you wish to use any of the ``run()`` methods.
(Likewise, you must manually set ``DAZzle.LayoutDirectory`` if you want layout
paths to be automatically adjusted.)

On the Mac, the ``exe_path`` should be set to a program that takes a single
XML filename as an argument.  The Mac ``endiciatool`` program probably will
not work on its own, without a wrapper shell script of some kind; I'm open to
suggestions as to how to improve this.  (Note, by the way, that the Mac client
doesn't support all of the options that the Windows client does, so remember
that use of PyDicia is entirely at your own risk, whatever the platform!)

On other platforms, the main usefulness of PyDicia would be in generating XML
for users to download (e.g. from a web application) or submitting and
processing jobs via a Samba-mounted queue directory.  You don't need an
``exe_path`` for this, but you will need to generate your own layout and output
file paths using ``Option`` objects, to avoid them being mangled by PyDicia's
platform-specific path munging.

XXX explain how to do that, or make it work anyway


Advanced Customization
======================

XXX Using Option elements, add_to_package()


-----------------
Options Reference
-----------------

Basic Package Options
=====================

XXX MailClass(text), NoPostage
DateAdvance(), Today, Tomorrow
Value()
Description()
WeightOz()


Addresses
=========

::
    >>> ToName("Phillip J. Eby")
    ToName('Phillip J. Eby')

    >>> ToTitle("President")
    ToTitle('President')

    >>> ToCompany("Dirt Simple, Inc.")
    ToCompany('Dirt Simple, Inc.')


XXX ToAddress(\*lines)
ToCity(text), ToState(text), ToPostalCode(text), ToZIP4(text), ToCountry(text)

XXX ReturnAddress(\*lines)
ToDeliveryPoint(text)
EndorsementLine(text)
ToCarrierRoute(text)


Package Details
===============

XXX PackageType()
FlatRateEnvelope
FlatRateBox
RectangularParcel
NonRectangularParcel
Postcard
Flat
Envelope
Width(), Length(), Depth()
NonMachinable
BalloonRate


Service Options
===============

XXX ReplyPostage
Stealth
SignatureWaiver
NoWeekendDelivery
NoHolidayDelivery
ReturnToSender
Insurance.USPS
Insurance.Endicia
Insurance.UPIC
Insurance.NONE
Services.RegisteredMail
Services.CertifiedMail
Services.RestrictedDelivery
Services.CertificateOfMailing
Services.ReturnReceipt
Services.DeliveryConfirmation
Services.SignatureConfirmation
Services.COD
Services.InsuredMail()


Customs Forms
=============

When processing international shipments, you will usually need to specify a
customs form, contents type, and items.  Additionally, if you want to print
the customs forms already "signed", you can specify a signer and the
certification option.

Contents Types
--------------

The ``ContentsType`` constructor defines the type of contents declared on the
customs form.  There are six predefined constants for the standard contents
types::

    >>> Customs.Sample
    ContentsType('SAMPLE')

    >>> Customs.Gift
    ContentsType('GIFT')

    >>> Customs.Documents
    ContentsType('DOCUMENTS')

    >>> Customs.Other
    ContentsType('OTHER')

    >>> Customs.Merchandise
    ContentsType('MERCHANDISE')

    >>> Customs.ReturnedGoods
    ContentsType('RETURNEDGOODS')


Customs Form Types
------------------

The ``CustomsFormType`` constructor defines the type of customs form to be
used.  There are four predefined constants for the allowed form types::

    >>> Customs.GEM
    CustomsFormType('GEM')

    >>> Customs.CN22
    CustomsFormType('CN22')

    >>> Customs.CP72
    CustomsFormType('CP72')

    >>> Customs.NONE
    CustomsFormType('NONE')


Customs Items
-------------

Items to be declared on a customs form are created using ``Customs.Item``.
The minimum required arguments are a description, a unit weight in ounces
(which must be an integer or decimal), and a value in US dollars (also an
integer or decimal)::

    >>> from decimal import Decimal
    >>> i = Customs.Item("Paperback book", 12, Decimal('29.95'))

You may also optionally specify a quantity (which must be an integer) and a
country of origin.  The defaults for these are ``1`` and ``"United States"``,
respectively::

    >>> i
    Item('Paperback book', Decimal("12"), Decimal("29.95"), 1, 'United States')

You always specify a unit weight and value; these are automatically multiplied
by the quantity on the customs form, and for purposes of calculating total
weight/value.

Note that a package's total weight must be greater than or equal to the sum of
its items' weight, and its value must exactly equal the sum of its items'
values::

    >>> b = Batch()
    >>> b.add_package(i)
    Traceback (most recent call last):
      ...
    OptionConflict: Total package weight must be specified when Customs.Items
                    are used

    >>> b.add_package(i, WeightOz(1))
    Traceback (most recent call last):
      ...
    OptionConflict: Total item weight is 12 oz, but
                    total package weight is only 1 oz

    >>> b.add_package(i, WeightOz(12), Value(69))
    Traceback (most recent call last):
      ...
    OptionConflict: Can't set 'Value=29.95' when 'Value=69' already set

And a form type and contents type must be specified if you include any items::

    >>> b.add_package(i, WeightOz(12))
    Traceback (most recent call last):
      ...
    OptionConflict: Customs form + content type must be specified with items

    >>> b.add_package(i, WeightOz(12), Customs.Gift)
    Traceback (most recent call last):
      ...
    OptionConflict: Customs form + content type must be specified with items

    >>> b.add_package(i, WeightOz(12), Customs.CN22)
    Traceback (most recent call last):
      ...
    OptionConflict: Customs form + content type must be specified with items

    >>> b.add_package(i, WeightOz(12), Customs.Gift, Customs.CN22)
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <CustomsQuantity1>1</CustomsQuantity1>
            <CustomsCountry1>United States</CustomsCountry1>
            <CustomsDescription1>Paperback book</CustomsDescription1>
            <CustomsWeight1>12</CustomsWeight1>
            <CustomsValue1>29.95</CustomsValue1>
            <WeightOz>12</WeightOz>
            <ContentsType>GIFT</ContentsType>
            <CustomsFormType>CN22</CustomsFormType>
            <Value>29.95</Value>
        </Package>
    </DAZzle>

The final customs form will include the multiplied-out weights and values based
on the quantity of each item::

    >>> b = Batch()
    >>> b.add_package(
    ...     Customs.Item('x',23,42,3), Customs.Item('y',1,7),
    ...     WeightOz(99), Customs.Gift, Customs.CN22
    ... )
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <CustomsQuantity1>3</CustomsQuantity1>
            <CustomsCountry1>United States</CustomsCountry1>
            <CustomsDescription1>x</CustomsDescription1>
            <CustomsWeight1>69</CustomsWeight1>
            <CustomsValue1>126</CustomsValue1>
            <CustomsQuantity2>1</CustomsQuantity2>
            <CustomsCountry2>United States</CustomsCountry2>
            <CustomsDescription2>y</CustomsDescription2>
            <CustomsWeight2>1</CustomsWeight2>
            <CustomsValue2>7</CustomsValue2>
            <WeightOz>99</WeightOz>
            <ContentsType>GIFT</ContentsType>
            <CustomsFormType>CN22</CustomsFormType>
            <Value>133</Value>
        </Package>
    </DAZzle>


Customs Signature
-----------------

You can specify the person who's certifying the customs form using these
options::

    >>> Customs.Signer("Phillip Eby")
    CustomsSigner('Phillip Eby')

    >>> Customs.Certify
    CustomsCertify('TRUE')



Processing Options
==================

XXX DAZzle.Test
DAZzle.Layout(filename)
DAZzle.OutputFile(filename)
DAZzle.Print
DAZzle.Verify
DAZzle.SkipUnverified
DAZzle.AutoClose
DAZzle.Prompt
DAZzle.AbortOnError
DAZzle.AutoPrintCustomsForms
DAZzle.XMLDirectory
DAZzle.LayoutDirectory
DAZzle.exe_path


Miscellaneous
=============

XXX RubberStamp(n, text)
ReferenceID(text)
CostCenter(int)



-------------------
Internals and Tests
-------------------

Misc imports for tests::

    >>> from pydicia import add_to_package, ET, Option, Batch, Package

Packages::

    >>> b = Batch()
    >>> p = Package(b)

    >>> print b.tostring()
    <DAZzle>
        <Package ID="1" />
    </DAZzle>

    >>> Box = Option('FlatRate', 'BOX')
    >>> add_to_package(Box, p, False)

    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <FlatRate>BOX</FlatRate>
        </Package>
    </DAZzle>

    >>> Envelope = Option('FlatRate', 'TRUE')
    >>> add_to_package(Envelope, p, False)
    Traceback (most recent call last):
      ...
    OptionConflict: Can't set 'FlatRate=TRUE' when 'FlatRate=BOX' already set

    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <FlatRate>BOX</FlatRate>
        </Package>
    </DAZzle>

    >>> add_to_package(Box, p, False)
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <FlatRate>BOX</FlatRate>
        </Package>
    </DAZzle>

    >>> add_to_package(Envelope, p, True)
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1">
            <FlatRate>BOX</FlatRate>
        </Package>
    </DAZzle>

    >>> del p.element[-1]; p.element.text=''
    >>> print b.tostring()
    <DAZzle>
        <Package ID="1" />
    </DAZzle>

    >>> verify_zip = Option('DAZzle', 'DAZ', 'Start')

    >>> add_to_package(verify_zip, p, False)
    >>> print b.tostring()
    <DAZzle Start="DAZ">
        <Package ID="1" />
    </DAZzle>

    >>> add_to_package(Option('DAZzle', 'PRINTING', 'Start'), p, False)
    Traceback (most recent call last):
      ...
    OptionConflict: Can't set 'DAZzle.Start=PRINTING' when 'DAZzle.Start=DAZ' already set

    >>> b = Batch()
    >>> p = Package(b)
    >>> add_to_package([verify_zip, Envelope], p, False)
    >>> print b.tostring()
    <DAZzle Start="DAZ">
        <Package ID="1">
            <FlatRate>TRUE</FlatRate>
        </Package>
    </DAZzle>

    >>> p.should_queue(Services.COD)
    True
    >>> print b.tostring()
    <DAZzle Start="DAZ">
        <Package ID="1">
            <FlatRate>TRUE</FlatRate>
        </Package>
    </DAZzle>

    >>> p.finish()
    >>> print b.tostring()
    <DAZzle Start="DAZ">
        <Package ID="1">
            <FlatRate>TRUE</FlatRate>
            <Services COD="ON" />
        </Package>
    </DAZzle>

    >>> p.should_queue(Services.COD)
    False


Batch rollback::

    >>> b = Batch()
    >>> print b.tostring()
    <DAZzle />

    >>> b.add_package(FlatRateEnvelope, FlatRateBox)
    Traceback (most recent call last):
      ...
    OptionConflict: Can't set 'PackageType=FLATRATEBOX' when
                               'PackageType=FLATRATEENVELOPE' already set

    >>> print b.tostring()  # rollback on error
    <DAZzle />


Misc shipment and postprocessing::

    >>> s = Shipment(verify_zip)
    >>> s.add_package(Box)
    >>> s.add_package(Envelope)
    >>> root, = s.batches
    >>> print root.tostring()
    <DAZzle Start="DAZ">
        <Package ID="1">
            <FlatRate>BOX</FlatRate>
        </Package>
        <Package ID="2">
            <FlatRate>TRUE</FlatRate>
        </Package>
    </DAZzle>

Option inversion::

    >>> ~Envelope
    FlatRate('FALSE')
    >>> ~~Envelope
    FlatRate('TRUE')

    >>> ~Option('Services', 'ON', 'RegisteredMail')
    Services.RegisteredMail('OFF')
    >>> ~~Option('Services', 'ON', 'RegisteredMail')
    Services.RegisteredMail('ON')

    >>> ~Option('DAZzle', 'YES', 'Prompt')
    DAZzle.Prompt('NO')
    >>> ~~Option('DAZzle', 'YES', 'Prompt')
    DAZzle.Prompt('YES')


The ``iter_options()`` generic function yields "option" objects for an
application object.  The default implementation is to raise an error::

    >>> from pydicia import iter_options

    >>> iter_options(27)
    Traceback (most recent call last):
      ...
    NotImplementedError: ('No option producer registered for', <type 'int'>)

And for lists and tuples, the default is to yield their contents::

    >>> list(iter_options((1, 2, 3)))
    [1, 2, 3]

    >>> list(iter_options(['a', 'b']))
    ['a', 'b']

This routine is used internally by ``add_to_package()``.