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Joined 1 year ago
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Cake day: June 20th, 2023

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  • A list comprehension is used to convert and/or filter elements of another iterable, in your case a range but this could also be another list. So you can think of it as taking one list, filtering/converting each element and producing a new list as a result.

    So there’s no need to append to any list as that’s implicit in the comprehension.

    For example, to produce a list of all squares in a range you could do:

    [x*x for x in range(10)]
    

    This would automatically “append” each square to the resulting list, there’s no need to do that yourself.





  • Here’s my Python script, it requires Python 3 and requests: -

    from argparse import ArgumentParser, Namespace
    import re
    import requests
    import time
    
    
    def get_arg_parser() -> ArgumentParser:
        parser = ArgumentParser(
            description="Copy community follows from one Lemmy instance to another"
        )
        parser.add_argument(
            "--source-url",
            dest="source_url",
            type=str,
            required=True,
            help="Base URL of the source instance from which to copy (e.g. https://lemmy.ml)"
        )
        parser.add_argument(
            "--dest-url",
            dest="dest_url",
            type=str,
            required=True,
            help="Base URL of the destination instance to which to copy (e.g. https://lemmy.world)"
        )
        parser.add_argument(
            "--source-jwt",
            dest="source_jwt",
            type=str,
            required=True,
            help="The JWT (login token) for the source instance"
        )
        parser.add_argument(
            "--dest-jwt",
            dest="dest_jwt",
            type=str,
            required=True,
            help="The JWT (login token) for the destination instance"
        )
        return parser
    
    
    def parse_args() -> Namespace:
        return get_arg_parser().parse_args()
    
    
    def get_followed_communities(args: Namespace) -> list:
        print(f"Fetching list of followed communities from {args.source_url}...")
        res = requests.get(
            f"{args.source_url}/api/v3/site",
            params={
                "auth": args.source_jwt,
            }
        )
        res.raise_for_status()
        res_data = res.json()
        if not res_data.get("my_user"):
            raise Exception("No my_user in site response")
        if not res_data["my_user"].get("follows"):
            raise Exception("No follows in my_user response")
        return res.json()["my_user"]["follows"]
    
    
    def find_community(name: str, args: Namespace) -> dict:
        res = requests.get(
            f"{args.dest_url}/api/v3/community",
            params={
                "name": name,
                "auth": args.dest_jwt,
            }
        )
        res.raise_for_status()
        res_data = res.json()
        if not res_data.get("community_view"):
            raise Exception("No community_view in community response")
        return res_data["community_view"]
    
    
    def follow_community(cid: int, args: Namespace) -> dict:
        res = requests.post(
            f"{args.dest_url}/api/v3/community/follow",
            json={
                "community_id": cid,
                "follow": True,
                "auth": args.dest_jwt,
            }
        )
        res.raise_for_status()
        return res.json()
    
    
    def get_qualified_name(actor_id: str):
        matches = re.search(r"https://(.*?)/(c|m)/(.*)", actor_id)
        if not matches:
            return actor_id
        groups = matches.groups()
        if len(groups) != 3:
            return actor_id
        return f"{groups[2]}@{groups[0]}"
    
    
    def sync_follow(follow: dict, args: Namespace):
        qn = get_qualified_name(follow["community"]["actor_id"])
        while True:
            try:
                community = find_community(qn, args)
                print(f"Subscription to {qn} is {community['subscribed']}")
                if community["subscribed"] == "NotSubscribed":
                    print(f"Following {qn} on {args.dest_url}...")
                    follow_community(community["community"]["id"], args)
                break
            except requests.exceptions.HTTPError as ex:
                if ex.response.status_code >= 500 and ex.response.status_code < 600:
                    print(f"WARNING: HTTP error {str(ex)}: trying again...")
                else:
                    print(f"WARNING: HTTP error {str(ex)}")
                    break
    
    
    def main():
        args = parse_args()
    
        try:
            follows = get_followed_communities(args)
        except Exception as ex:
            print(f"ERROR: unable to fetch followed communities from {args.source_url}: {str(ex)}")
            return
    
        print(f"Syncing {len(follows)} followed communities to {args.dest_url}...")
        with open("failures.txt", "wt") as failures:
            for follow in follows:
                try:
                    sync_follow(follow, args)
                except Exception as ex:
                    print(f"ERROR: {str(ex)}")
                    failures.write(
                        get_qualified_name(
                            follow["community"]["actor_id"]
                        )
                    )
                time.sleep(1)
    
    
    if __name__ == "__main__":
        main()
    

    You use it like this (for example), assuming it’s saved to sync.py: -

    python sync.py --source-url=https://lemmy.ml --dest-url=https://lemmy.world --source-jwt=abc123 --dest-jwt=bcd234