Issue #14814: Add a basic ipaddress tutorial (thanks to Sandro Tosi for the initial conversion from Peter Moody's wiki version)

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+.. _ipaddress-howto:
+
+***************
+Ipaddress Howto
+***************
+
+:author: Peter Moody
+
+.. topic:: Abstract
+
+   This document is a gentle introduction to :mod:`ipaddress` module.
+
+
+Creating Address/Network/Interface objects
+==========================================
+
+Since :mod:`ipaddress` is a module for inspecting and manipulating IP address,
+the first thing you'll want to do is create some objects.  You can use
+:mod:`ipaddress` to create objects from strings and integers.
+
+
+A Note on IP Versions
+---------------------
+
+For readers that aren't particularly familiar with IP addressing, it's
+important to know that the Internet Protocol is currently in the process
+of moving from version 4 of the protocol to version 6. This transition is
+occurring largely because version 4 of the protocol doesn't provide enough
+addresses to handle the needs of the whole world, especially given the
+increasing number of devices with direct connections to the internet.
+
+Explaining the details of the differences between the two versions of the
+protocol is beyond the scope of this introduction, but readers need to at
+least be aware that these two versions exist, and it will sometimes be
+necessary to force the use of one version or the other.
+
+
+IP Host Addresses
+-----------------
+
+Addresses, often referred to as "host addresses" are the most basic unit
+when working with IP addressing. The simplest way to create addresses is
+to use the ``ip_address`` factory function, which automatically determines
+whether to create an IPv4 or IPv6 address based on the passed in value::
+
+   >>> ipaddress.ip_address('192.0.2.1')
+   IPv4Address('192.0.2.1')
+   >>> ipaddress.ip_address('2001:DB8::1')
+   IPv6Address('2001:db8::1')
+
+Addresses can also be created directly from integers. Values that will
+fit within 32 bits are assumed to be IPv4 addresses::
+
+   >>> ipaddress.ip_address(3221225985)
+   IPv4Address('192.0.2.1')
+   >>> ipaddress.ip_address(42540766411282592856903984951653826561)
+   IPv6Address('2001:db8::1')
+
+To force the use of IPv4 or IPv6 addresses, the relevant classes can be
+invoked directly. This is particularly useful to force creation of IPv6
+addresses for small integers::
+
+   >>> ipaddress.ip_address(1)
+   IPv4Address('0.0.0.1')
+   >>> ipaddress.IPv4Address(1)
+   IPv4Address('0.0.0.1')
+   >>> ipaddress.IPv6Address(1)
+   IPv6Address('::1')
+
+
+Defining Networks
+-----------------
+
+Host addresses are usually grouped together into IP networks, so
+:mod:`ipaddress` provides a way to create, inspect and manipulate network
+definitions. IP network objects are constructed from strings that define the
+range of host addresses that are part of that network. The simplest form
+for that information is a "network address/network prefix" pair, where the
+prefix defines the number of leading bits that are compared to determine
+whether or not an address is part of the network and the network address
+defines the expected value of those bits.
+
+As for addresses, a factory function is provided that determines the correct
+IP version automatically::
+
+   >>> ipaddress.ip_network('192.0.2.0/24')
+   IPv4Network('192.0.2.0/24')
+   >>> ipaddress.ip_network('2001:db8::0/96')
+   IPv6Network('2001:db8::/96')
+
+Network objects cannot have any host bits set.  The practical effect of this
+is that ``192.0.2.1/24`` does not describe a network.  Such definitions are
+referred to as interface objects since the ip-on-a-network notation is
+commonly used to describe network interfaces of a computer on a given network
+and are described further in the next section.
+
+By default, attempting to create a network object with host bits set will
+result in :exc:`ValueError` being raised. To request that the
+additional bits instead be coerced to zero, the flag ``strict=False`` can
+be passed to the constructor::
+
+   >>> ipaddress.ip_network('192.0.2.1/24')
+   Traceback (most recent call last):
+      ...
+   ValueError: 192.0.2.1/24 has host bits set
+   >>> ipaddress.ip_network('192.0.2.1/24', strict=False)
+   IPv4Network('192.0.2.0/24')
+
+While the string form offers significantly more flexibility, networks can
+also be defined with integers, just like host addresses. In this case, the
+network is considered to contain only the single address identified by the
+integer, so the network prefix includes the entire network address::
+
+   >>> ipaddress.ip_network(3221225984)
+   IPv4Network('192.0.2.0/32')
+   >>> ipaddress.ip_network(42540766411282592856903984951653826560L)
+   IPv6Network('2001:db8::/128')
+
+Creation of a particular kind of network can be forced by calling the
+class constructor directly instead of using the factory function.
+
+
+Host Interfaces
+---------------
+
+As mentioned just above, if you need to describe an address on a particular
+network, neither the address nor the network classes are sufficient.
+Notation like ``192.0.2.1/24`` is commonly used network engineers and the
+people who write tools for firewalls and routers as shorthand for "the host
+``192.0.2.1`` on the network ``192.0.2.0/24``", Accordingly, :mod:`ipaddress`
+provides a set of hybrid classes that associate an address with a particular
+network. The interface for creation is identical to that for defining network
+objects, except that the address portion isn't constrained to being a network
+address.
+
+   >>> ipaddress.ip_interface('192.0.2.1/24')
+   IPv4Interface('192.0.2.1/24')
+   >>> ipaddress.ip_network('2001:db8::1/96')
+   IPv6Interface('2001:db8::1/96')
+
+Integer inputs are accepted (as with networks), and use of a particular IP
+version can be forced by calling the relevant constructor directly.
+
+
+Inspecting Address/Network/Interface Objects
+============================================
+
+You've gone to the trouble of creating an IPv(4|6)(Address|Network|Interface)
+object, so you probably want to get information about it.  :mod:`ipaddress`
+tries to make doing this easy and intuitive.
+
+Extracting the IP version::
+
+   >>> addr4 = ipaddress.ip_address('192.0.2.1')
+   >>> addr6 = ipaddress.ip_address('2001:db8::1')
+   >>> addr6.version
+   6
+   >>> addr4.version
+   4
+
+Obtaining the network from an interface::
+
+   >>> host4 = ipaddress.ip_interface('192.0.2.1/24')
+   >>> host4.network
+   IPv4Network('192.0.2.0/24')
+   >>> host6 = ipaddress.ip_interface('2001:db8::1/96')
+   >>> host6.network
+   IPv6Network('2001:db8::/96')
+
+Finding out how many individual addresses are in a network::
+
+   >>> net4 = ipaddress.ip_network('192.0.2.0/24')
+   >>> net4.numhosts
+   256
+   >>> net6 = ipaddress.ip_network('2001:db8::0/96')
+   >>> net6.numhosts
+   4294967296
+
+Iterating through the 'usable' addresses on a network::
+
+   >>> net4 = ipaddress.ip_network('192.0.2.0/24')
+   >>> for x in net4.iterhosts():
+          print(x)
+   192.0.2.1
+   192.0.2.2
+   192.0.2.3
+   192.0.2.4
+   <snip>
+   192.0.2.252
+   192.0.2.253
+   192.0.2.254
+
+
+Obtaining the netmask (i.e. set bits corresponding to the network prefix) or
+the hostmask (any bits that are not part of the netmask):
+
+   >>> net4 = ipaddress.ip_network('192.0.2.0/24')
+   >>> net4.netmask
+   IPv4Address('255.255.255.0')
+   >>> net4.hostmask
+   IPv4Address('0.0.0.255')
+   >>> net6 = ipaddress.ip_network('2001:db8::0/96')
+   >>> net6.netmask
+   IPv6Address('ffff:ffff:ffff:ffff:ffff:ffff::')
+   >>> net6.hostmask
+   IPv6Address('::ffff:ffff')
+
+
+Exploding or compressing the address::
+
+   >>> net6.exploded
+   '2001:0000:0000:0000:0000:0000:0000:0000/96'
+   >>> addr6.exploded
+   '2001:0000:0000:0000:0000:0000:0000:0001'
+
+
+Networks as lists of Addresses
+==============================
+
+It's sometimes useful to treat networks as lists.  This means it is possible
+to index them like this::
+
+   >>> net4[1]
+   IPv4Address('192.0.2.1')
+   >>> net4[-1]
+   IPv4Address('192.0.2.255')
+   >>> net6[1]
+   IPv6Address('2001::1')
+   >>> net6[-1]
+   IPv6Address('2001::ffff:ffff')
+
+
+It also means that network objects lend themselves to using the list
+membership test syntax like this::
+
+   if address in network:
+       # do something
+
+Containment testing is done efficiently based on the network prefix::
+
+   >>> addr4 = ipaddress.ip_address('192.0.2.1')
+   >>> addr4 in ipaddress.ip_network('192.0.2.0/24')
+   True
+   >>> addr4 in ipaddress.ip_network('192.0.3.0/24')
+   False
+
+
+Comparisons
+===========
+
+:mod:`ipaddress` provides some simple, hopefully intuitive ways to compare
+objects, where it makes sense::
+
+   >>> ipaddress.ip_address('192.0.2.1') < ipaddress.ip_address('192.0.2.2')
+   True
+
+A :exc:`TypeError` exception is raised if you try to compare objects of
+different versions or different types.
+
+
+Using IP Addresses with other modules
+=====================================
+
+Other modules that use IP addresses (such as :mod:`socket`) usually won't
+accept objects from this module directly. Instead, they must be coerced to
+an integer or string that the other module will accept::
+
+   >>> addr4 = ipaddress.ip_address('192.0.2.1')
+   >>> str(addr4)
+   '192.0.2.1'
+   >>> int(addr4)
+   3221225985
+
+
+Exceptions raised by :mod:`ipaddress`
+=====================================
+
+If you try to create an address/network/interface object with an invalid value
+for either the address or netmask, :mod:`ipaddress` will raise an
+:exc:`AddressValueError` or :exc:`NetmaskValueError` respectively. However,
+this applies only when calling the class constructors directly. The factory
+functions and other module level functions will just raise :exc:`ValueError`.
+
+Both of the module specific exceptions have :exc:`ValueError` as their
+parent class, so if you're not concerned with the particular type of error,
+you can still do the following::
+
+   try:
+       ipaddress.IPv4Address(address)
+   except ValueError:
+       print 'address/netmask is invalid: %s' % address