This recipe code uses a low-level socket feature to find out the interfaces present on the system. The single list_interfaces() method creates a socket object and finds the network interface information from manipulating this object. It does so by making a call to the fnctl module's ioctl() method. The fnctl module interfaces with some Unix routines, for example, fnctl(). This interface performs an I/O control operation on the underlying file descriptor socket, which is obtained by calling the fileno() method of the socket object.

The additional parameter of the ioctl() method includes the SIOCGIFADDR constant defined in the C socket library and a data structure produced by the struct module's pack() function. The memory address specified by a data structure is modified as a result of the ioctl() call. In this case, the interface_names variable holds this information. After unpacking the sock_info return value of the ioctl() call, the number of network interfaces is increased twice if the size of the data suggests it. This is done in a while loop to discover all interfaces if our initial interface count assumption is not correct.

The names of interfaces are extracted from the string format of the interface_names variable. It reads specific fields of that variable and appends the values in the interfaces' list. At the end of the list_interfaces() function, this is returned.