I'd like to parse status.dat file for nagios3 and output as xml with a python script. The xml part is the easy one but how do I go about parsing the file? Use multi line regex? It's possible the file will be large as many hosts and services are monitored, will loading the whole file in memory be wise?
I only need to extract services that have critical state and host they belong to.

Any help and pointing in the right direction will be highly appreciated.

LE Here's how the file looks:

########################################
#          NAGIOS STATUS FILE
#
# THIS FILE IS AUTOMATICALLY GENERATED
# BY NAGIOS.  DO NOT MODIFY THIS FILE!
########################################

info {
    created=1233491098
    version=2.11
    }

program {
    modified_host_attributes=0
    modified_service_attributes=0
    nagios_pid=15015
    daemon_mode=1
    program_start=1233490393
    last_command_check=0
    last_log_rotation=0
    enable_notifications=1
    active_service_checks_enabled=1
    passive_service_checks_enabled=1
    active_host_checks_enabled=1
    passive_host_checks_enabled=1
    enable_event_handlers=1
    obsess_over_services=0
    obsess_over_hosts=0
    check_service_freshness=1
    check_host_freshness=0
    enable_flap_detection=0
    enable_failure_prediction=1
    process_performance_data=0
    global_host_event_handler=
    global_service_event_handler=
    total_external_command_buffer_slots=4096
    used_external_command_buffer_slots=0
    high_external_command_buffer_slots=0
    total_check_result_buffer_slots=4096
    used_check_result_buffer_slots=0
    high_check_result_buffer_slots=2
    }

host {
    host_name=localhost
    modified_attributes=0
    check_command=check-host-alive
    event_handler=
    has_been_checked=1
    should_be_scheduled=0
    check_execution_time=0.019
    check_latency=0.000
    check_type=0
    current_state=0
    last_hard_state=0
    plugin_output=PING OK - Packet loss = 0%, RTA = 3.57 ms
    performance_data=
    last_check=1233490883
    next_check=0
    current_attempt=1
    max_attempts=10
    state_type=1
    last_state_change=1233489475
    last_hard_state_change=1233489475
    last_time_up=1233490883
    last_time_down=0
    last_time_unreachable=0
    last_notification=0
    next_notification=0
    no_more_notifications=0
    current_notification_number=0
    notifications_enabled=1
    problem_has_been_acknowledged=0
    acknowledgement_type=0
    active_checks_enabled=1
    passive_checks_enabled=1
    event_handler_enabled=1
    flap_detection_enabled=1
    failure_prediction_enabled=1
    process_performance_data=1
    obsess_over_host=1
    last_update=1233491098
    is_flapping=0
    percent_state_change=0.00
    scheduled_downtime_depth=0
    }

service {
    host_name=gateway
    service_description=PING
    modified_attributes=0
    check_command=check_ping!100.0,20%!500.0,60%
    event_handler=
    has_been_checked=1
    should_be_scheduled=1
    check_execution_time=4.017
    check_latency=0.210
    check_type=0
    current_state=0
    last_hard_state=0
    current_attempt=1
    max_attempts=4
    state_type=1
    last_state_change=1233489432
    last_hard_state_change=1233489432
    last_time_ok=1233491078
    last_time_warning=0
    last_time_unknown=0
    last_time_critical=0
    plugin_output=PING OK - Packet loss = 0%, RTA = 2.98 ms
    performance_data=
    last_check=1233491078
    next_check=1233491378
    current_notification_number=0
    last_notification=0
    next_notification=0
    no_more_notifications=0
    notifications_enabled=1
    active_checks_enabled=1
    passive_checks_enabled=1
    event_handler_enabled=1
    problem_has_been_acknowledged=0
    acknowledgement_type=0
    flap_detection_enabled=1
    failure_prediction_enabled=1
    process_performance_data=1
    obsess_over_service=1
    last_update=1233491098
    is_flapping=0
    percent_state_change=0.00
    scheduled_downtime_depth=0
    }

It can have any number of hosts and a host can have any number of services.