Python: Enumerating IP Addresses on MacOS X

How do you enumerate the host's local IP addresses from python? This turns out to be a surprisingly common question. Unfortunately, there is no pretty answer; it depends on the host operating system. On Windows, you can wrap the IP Helper GetIpAddrTable using ctypes. On modern Linux, *BSD, or MacOS X systems, you can wrap getifaddrs(). Neither is trivial, though, so I'll save those for a future post.

Luckily, MacOS X provides a simpler way to get the local IP addresses: the system configuration dynamic store. Using pyObjC, which comes pre-installed on every Mac, we can write a straight port of Apple's example in Technical Note TN1145 for retrieving a list of all IPv4 addresses assigned to local interfaces:

from SystemConfiguration import *    # from pyObjC
import socket

def GetIPv4Addresses():
    """
    Get all IPv4 addresses assigned to local interfaces.
    Returns a generator object that produces information
    about each IPv4 address present at the time that the
    function was called.

    For each IPv4 address, the returned generator yields
    a tuple consisting of the interface name, address
    family (always socket.AF_INET), the IP address, and
    the netmask.  The tuple elements may also be accessed
    by the names: "ifname", "family", "address", and
    "netmask".
    """
    ds = SCDynamicStoreCreate(None, 'GetIPv4Addresses', None, None)
    # Get all keys matching pattern State:/Network/Service/[^/]+/IPv4
    pattern = SCDynamicStoreKeyCreateNetworkServiceEntity(None,
                                                          kSCDynamicStoreDomainState,
                                                          kSCCompAnyRegex,
                                                          kSCEntNetIPv4)
    patterns = CFArrayCreate(None, (pattern, ), 1, kCFTypeArrayCallBacks)
    valueDict = SCDynamicStoreCopyMultiple(ds, None, patterns)

    ipv4info = namedtuple('ipv4info', 'ifname family address netmask')

    for serviceDict in valueDict.values():
        ifname = serviceDict[u'InterfaceName']
        for address, netmask in zip(serviceDict[u'Addresses'], serviceDict[u'SubnetMasks']):
            yield ipv4info(ifname, socket.AF_INET, address, netmask)

One interesting point regarding this code is that it doesn't actually inspect interface information in the system configuration dynamic store. The interface-related keys are stored under State:/Network/Interface/, but this code (and Apple's example on which it is based) inspect keys under State:/Network/Service/ instead. However, if you want to get IPv6 addresses then you do have to inspect the system configuration's interface information:

from SystemConfiguration import *    # from pyObjC
import socket
import re
ifnameExtractor = re.compile(r'/Interface/([^/]+)/')

def GetIPv6Addresses():
    """
    Get all IPv6 addresses assigned to local interfaces.
    Returns a generator object that produces information
    about each IPv6 address present at the time that the
    function was called.
    
    For each IPv6 address, the returned generator yields
    a tuple consisting of the interface name, address
    family (always socket.AF_INET6), the IP address, and
    the prefix length.  The tuple elements may also be
    accessed by the names: "ifname", "family", "address",
    and "prefixlen".
    """
    ds = SCDynamicStoreCreate(None, 'GetIPv6Addresses', None, None)
    # Get all keys matching pattern State:/Network/Interface/[^/]+/IPv6
    pattern = SCDynamicStoreKeyCreateNetworkInterfaceEntity(None,
                                                          kSCDynamicStoreDomainState,
                                                          kSCCompAnyRegex,
                                                          kSCEntNetIPv6)
    patterns = CFArrayCreate(None, (pattern, ), 1, kCFTypeArrayCallBacks)
    valueDict = SCDynamicStoreCopyMultiple(ds, None, patterns)

    ipv6info = namedtuple('ipv6info', 'ifname family address prefixlen')

    for key, ifDict in valueDict.items():
        ifname = ifnameExtractor.search(key).group(1)
        for address, prefixlen in zip(ifDict[u'Addresses'], ifDict[u'PrefixLength']):
            yield ipv6info(ifname, socket.AF_INET6, address, prefixlen)

In fact, you could easily adapt the above function to be able to fetch IPv4 addresses from the interface configuration.