IPv4 Address Iterator with CIDR Support

Problem Overview

You need to implement an IPv4 iterator class in Python that can iterate through IP addresses. The problem progressively adds complexity through multiple parts, starting with forward iteration, then backward iteration, and finally adding CIDR support.

Problem Statement

Implement an IPv4Iterator class in Python that can iterate through a range of IP addresses. The class should support the following functionalities:

1. Forward iteration: Iterate through IP addresses in ascending order.
2. Backward iteration: Iterate through IP addresses in descending order.
3. CIDR support: Support IP ranges specified in CIDR notation (e.g., "192.168.1.0/24").

The class should have the following methods:

• __init__(self, start_ip, end_ip, cidr=None): Initialize the iterator with the start and end IP addresses. If cidr is provided, use it to determine the range of IP addresses.
• __iter__(self): Return the iterator object itself.
• __next__(self): Return the next IP address in the range. If the end of the range is reached, raise a StopIteration exception.

Examples

`python

Forward iteration

iterator = IPv4Iterator("192.168.1.1", "192.168.1.10") for ip in iterator: print(ip)

Backward iteration

iterator = IPv4Iterator("192.168.1.10", "192.168.1.1") for ip in iterator: print(ip)

CIDR support

iterator = IPv4Iterator("192.168.1.0", "192.168.1.255", "192.168.1.0/24") for ip in iterator: print(ip) `

Constraints

• IP addresses should be in the standard dot-decimal notation (e.g., "192.168.1.1").
• The cidr parameter is optional and should only be used if provided.
• The iterator should handle invalid IP addresses and ranges gracefully.

Hints

• Use bitwise operations to manipulate IP addresses.
• Convert IP addresses to integers for easier comparison and manipulation.
• Use the ipaddress module in Python for CIDR support.

Solution

`python import ipaddress

class IPv4Iterator: def init(self, start_ip, end_ip, cidr=None): self.start_ip = ipaddress.IPv4Address(start_ip) self.end_ip = ipaddress.IPv4Address(end_ip) self.cidr = cidr self.current_ip = self.start_ip

def __iter__(self):
    return self

def __next__(self):
    if self.cidr:
        network = ipaddress.IPv4Network(self.cidr, strict=False)
        if self.current_ip not in network:
            raise StopIteration
    elif self.current_ip > self.end_ip:
        raise StopIteration

    result = str(self.current_ip)
    self.current_ip += 1
    return result

Example usage:

iterator = IPv4Iterator("192.168.1.1", "192.168.1.10") for ip in iterator: print(ip) `