参考 ultralytics/utils/downloads.py

def is_url(url, check=False):
    """
    Validates if the given string is a URL and optionally checks if the URL exists online.

    Args:
        url (str): The string to be validated as a URL.
        check (bool, optional): If True, performs an additional check to see if the URL exists online.
            Defaults to True.

    Returns:
        (bool): Returns True for a valid URL. If 'check' is True, also returns True if the URL exists online.
            Returns False otherwise.

    Example:
        ```python
        valid = is_url("https://www.example.com")
        ```
    """
    with contextlib.suppress(Exception):
        url = str(url)
        result = parse.urlparse(url)
        assert all([result.scheme, result.netloc])  # check if is url
        if check:
            with request.urlopen(url) as response:
                return response.getcode() == 200  # check if exists online
        return True
    return False

def delete_dsstore(path, files_to_delete=(".DS_Store", "__MACOSX")):
    """
    Deletes all ".DS_store" files under a specified directory.

    Args:
        path (str, optional): The directory path where the ".DS_store" files should be deleted.
        files_to_delete (tuple): The files to be deleted.

    Example:
        ```python
        from ultralytics.utils.downloads import delete_dsstore

        delete_dsstore('path/to/dir')
        ```

    Note:
        ".DS_store" files are created by the Apple operating system and contain metadata about folders and files. They
        are hidden system files and can cause issues when transferring files between different operating systems.
    """
    for file in files_to_delete:
        matches = list(Path(path).rglob(file))
        LOGGER.info(f"Deleting {file} files: {matches}")
        for f in matches:
            f.unlink()

def zip_directory(directory, compress=True, exclude=(".DS_Store", "__MACOSX"), progress=True):
    """
    Zips the contents of a directory, excluding files containing strings in the exclude list. The resulting zip file is
    named after the directory and placed alongside it.

    Args:
        directory (str | Path): The path to the directory to be zipped.
        compress (bool): Whether to compress the files while zipping. Default is True.
        exclude (tuple, optional): A tuple of filename strings to be excluded. Defaults to ('.DS_Store', '__MACOSX').
        progress (bool, optional): Whether to display a progress bar. Defaults to True.

    Returns:
        (Path): The path to the resulting zip file.

    Example:
        ```python
        from ultralytics.utils.downloads import zip_directory

        file = zip_directory('path/to/dir')
        ```
    """
    from zipfile import ZIP_DEFLATED, ZIP_STORED, ZipFile

    delete_dsstore(directory)
    directory = Path(directory)
    if not directory.is_dir():
        raise FileNotFoundError(f"Directory '{directory}' does not exist.")

    # Unzip with progress bar
    files_to_zip = [f for f in directory.rglob("*") if f.is_file() and all(x not in f.name for x in exclude)]
    zip_file = directory.with_suffix(".zip")
    compression = ZIP_DEFLATED if compress else ZIP_STORED
    with ZipFile(zip_file, "w", compression) as f:
        for file in TQDM(files_to_zip, desc=f"Zipping {directory} to {zip_file}...", unit="file", disable=not progress):
            f.write(file, file.relative_to(directory))

    return zip_file  # return path to zip file

def unzip_file(file, path=None, exclude=(".DS_Store", "__MACOSX"), exist_ok=False, progress=True):
    """
    Unzips a *.zip file to the specified path, excluding files containing strings in the exclude list.

    If the zipfile does not contain a single top-level directory, the function will create a new
    directory with the same name as the zipfile (without the extension) to extract its contents.
    If a path is not provided, the function will use the parent directory of the zipfile as the default path.

    Args:
        file (str): The path to the zipfile to be extracted.
        path (str, optional): The path to extract the zipfile to. Defaults to None.
        exclude (tuple, optional): A tuple of filename strings to be excluded. Defaults to ('.DS_Store', '__MACOSX').
        exist_ok (bool, optional): Whether to overwrite existing contents if they exist. Defaults to False.
        progress (bool, optional): Whether to display a progress bar. Defaults to True.

    Raises:
        BadZipFile: If the provided file does not exist or is not a valid zipfile.

    Returns:
        (Path): The path to the directory where the zipfile was extracted.

    Example:
        ```python
        from ultralytics.utils.downloads import unzip_file

        dir = unzip_file('path/to/file.zip')
        ```
    """
    from zipfile import BadZipFile, ZipFile, is_zipfile

    if not (Path(file).exists() and is_zipfile(file)):
        raise BadZipFile(f"File '{file}' does not exist or is a bad zip file.")
    if path is None:
        path = Path(file).parent  # default path

    # Unzip the file contents
    with ZipFile(file) as zipObj:
        files = [f for f in zipObj.namelist() if all(x not in f for x in exclude)]
        top_level_dirs = {Path(f).parts[0] for f in files}

        if len(top_level_dirs) > 1 or (len(files) > 1 and not files[0].endswith("/")):
            # Zip has multiple files at top level
            path = extract_path = Path(path) / Path(file).stem  # i.e. ../datasets/coco8
        else:
            # Zip has 1 top-level directory
            extract_path = path  # i.e. ../datasets
            path = Path(path) / list(top_level_dirs)[0]  # i.e. ../datasets/coco8

        # Check if destination directory already exists and contains files
        if path.exists() and any(path.iterdir()) and not exist_ok:
            # If it exists and is not empty, return the path without unzipping
            LOGGER.warning(f"WARNING ⚠️ Skipping {file} unzip as destination directory {path} is not empty.")
            return path

        for f in TQDM(files, desc=f"Unzipping {file} to {Path(path).resolve()}...", unit="file", disable=not progress):
            # Ensure the file is within the extract_path to avoid path traversal security vulnerability
            if ".." in Path(f).parts:
                LOGGER.warning(f"Potentially insecure file path: {f}, skipping extraction.")
                continue
            zipObj.extract(f, extract_path)

    return path  # return unzip dir

def check_disk_space(url="https://ultralytics.com/assets/coco128.zip", path=Path.cwd(), sf=1.5, hard=True):
    """
    Check if there is sufficient disk space to download and store a file.

    Args:
        url (str, optional): The URL to the file. Defaults to 'https://ultralytics.com/assets/coco128.zip'.
        path (str | Path, optional): The path or drive to check the available free space on.
        sf (float, optional): Safety factor, the multiplier for the required free space. Defaults to 2.0.
        hard (bool, optional): Whether to throw an error or not on insufficient disk space. Defaults to True.

    Returns:
        (bool): True if there is sufficient disk space, False otherwise.
    """
    try:
        r = requests.head(url)  # response
        assert r.status_code < 400, f"URL error for {url}: {r.status_code} {r.reason}"  # check response
    except Exception:
        return True  # requests issue, default to True

    # Check file size
    gib = 1 << 30  # bytes per GiB
    data = int(r.headers.get("Content-Length", 0)) / gib  # file size (GB)
    total, used, free = (x / gib for x in shutil.disk_usage(path))  # bytes

    if data * sf < free:
        return True  # sufficient space

    # Insufficient space
    text = (
        f"WARNING ⚠️ Insufficient free disk space {free:.1f} GB < {data * sf:.3f} GB required, "
        f"Please free {data * sf - free:.1f} GB additional disk space and try again."
    )
    if hard:
        raise MemoryError(text)
    LOGGER.warning(text)
    return False

def get_google_drive_file_info(link):
    """
    Retrieves the direct download link and filename for a shareable Google Drive file link.

    Args:
        link (str): The shareable link of the Google Drive file.

    Returns:
        (str): Direct download URL for the Google Drive file.
        (str): Original filename of the Google Drive file. If filename extraction fails, returns None.

    Example:
        ```python
        from ultralytics.utils.downloads import get_google_drive_file_info

        link = "https://drive.google.com/file/d/1cqT-cJgANNrhIHCrEufUYhQ4RqiWG_lJ/view?usp=drive_link"
        url, filename = get_google_drive_file_info(link)
        ```
    """
    file_id = link.split("/d/")[1].split("/view")[0]
    drive_url = f"https://drive.google.com/uc?export=download&id={file_id}"
    filename = None

    # Start session
    with requests.Session() as session:
        response = session.get(drive_url, stream=True)
        if "quota exceeded" in str(response.content.lower()):
            raise ConnectionError(
                emojis(
                    f"❌  Google Drive file download quota exceeded. "
                    f"Please try again later or download this file manually at {link}."
                )
            )
        for k, v in response.cookies.items():
            if k.startswith("download_warning"):
                drive_url += f"&confirm={v}"  # v is token
        cd = response.headers.get("content-disposition")
        if cd:
            filename = re.findall('filename="(.+)"', cd)[0]
    return drive_url, filename

def safe_download(
    url,
    file=None,
    dir=None,
    unzip=True,
    delete=False,
    curl=False,
    retry=3,
    min_bytes=1e0,
    exist_ok=False,
    progress=True,
):
    """
    Downloads files from a URL, with options for retrying, unzipping, and deleting the downloaded file.

    Args:
        url (str): The URL of the file to be downloaded.
        file (str, optional): The filename of the downloaded file.
            If not provided, the file will be saved with the same name as the URL.
        dir (str, optional): The directory to save the downloaded file.
            If not provided, the file will be saved in the current working directory.
        unzip (bool, optional): Whether to unzip the downloaded file. Default: True.
        delete (bool, optional): Whether to delete the downloaded file after unzipping. Default: False.
        curl (bool, optional): Whether to use curl command line tool for downloading. Default: False.
        retry (int, optional): The number of times to retry the download in case of failure. Default: 3.
        min_bytes (float, optional): The minimum number of bytes that the downloaded file should have, to be considered
            a successful download. Default: 1E0.
        exist_ok (bool, optional): Whether to overwrite existing contents during unzipping. Defaults to False.
        progress (bool, optional): Whether to display a progress bar during the download. Default: True.

    Example:
        ```python
        from ultralytics.utils.downloads import safe_download

        link = "https://ultralytics.com/assets/bus.jpg"
        path = safe_download(link)
        ```
    """
    gdrive = url.startswith("https://drive.google.com/")  # check if the URL is a Google Drive link
    if gdrive:
        url, file = get_google_drive_file_info(url)

    f = Path(dir or ".") / (file or url2file(url))  # URL converted to filename
    if "://" not in str(url) and Path(url).is_file():  # URL exists ('://' check required in Windows Python<3.10)
        f = Path(url)  # filename
    elif not f.is_file():  # URL and file do not exist
        desc = f"Downloading {url if gdrive else clean_url(url)} to '{f}'"
        LOGGER.info(f"{desc}...")
        f.parent.mkdir(parents=True, exist_ok=True)  # make directory if missing
        check_disk_space(url, path=f.parent)
        for i in range(retry + 1):
            try:
                if curl or i > 0:  # curl download with retry, continue
                    s = "sS" * (not progress)  # silent
                    r = subprocess.run(["curl", "-#", f"-{s}L", url, "-o", f, "--retry", "3", "-C", "-"]).returncode
                    assert r == 0, f"Curl return value {r}"
                else:  # urllib download
                    method = "torch"
                    if method == "torch":
                        torch.hub.download_url_to_file(url, f, progress=progress)
                    else:
                        with request.urlopen(url) as response, TQDM(
                            total=int(response.getheader("Content-Length", 0)),
                            desc=desc,
                            disable=not progress,
                            unit="B",
                            unit_scale=True,
                            unit_divisor=1024,
                        ) as pbar:
                            with open(f, "wb") as f_opened:
                                for data in response:
                                    f_opened.write(data)
                                    pbar.update(len(data))

                if f.exists():
                    if f.stat().st_size > min_bytes:
                        break  # success
                    f.unlink()  # remove partial downloads
            except Exception as e:
                if i == 0 and not is_online():
                    raise ConnectionError(emojis(f"❌  Download failure for {url}. Environment is not online.")) from e
                elif i >= retry:
                    raise ConnectionError(emojis(f"❌  Download failure for {url}. Retry limit reached.")) from e
                LOGGER.warning(f"⚠️ Download failure, retrying {i + 1}/{retry} {url}...")

    if unzip and f.exists() and f.suffix in {"", ".zip", ".tar", ".gz"}:
        from zipfile import is_zipfile

        unzip_dir = (dir or f.parent).resolve()  # unzip to dir if provided else unzip in place
        if is_zipfile(f):
            unzip_dir = unzip_file(file=f, path=unzip_dir, exist_ok=exist_ok, progress=progress)  # unzip
        elif f.suffix in {".tar", ".gz"}:
            LOGGER.info(f"Unzipping {f} to {unzip_dir}...")
            subprocess.run(["tar", "xf" if f.suffix == ".tar" else "xfz", f, "--directory", unzip_dir], check=True)
        if delete:
            f.unlink()  # remove zip
        return unzip_dir

def get_github_assets(repo="ultralytics/assets", version="latest", retry=False):
    """
    Retrieve the specified version's tag and assets from a GitHub repository. If the version is not specified, the
    function fetches the latest release assets.

    Args:
        repo (str, optional): The GitHub repository in the format 'owner/repo'. Defaults to 'ultralytics/assets'.
        version (str, optional): The release version to fetch assets from. Defaults to 'latest'.
        retry (bool, optional): Flag to retry the request in case of a failure. Defaults to False.

    Returns:
        (tuple): A tuple containing the release tag and a list of asset names.

    Example:
        ```python
        tag, assets = get_github_assets(repo='ultralytics/assets', version='latest')
        ```
    """

    if version != "latest":
        version = f"tags/{version}"  # i.e. tags/v6.2
    url = f"https://api.github.com/repos/{repo}/releases/{version}"
    r = requests.get(url)  # github api
    if r.status_code != 200 and r.reason != "rate limit exceeded" and retry:  # failed and not 403 rate limit exceeded
        r = requests.get(url)  # try again
    if r.status_code != 200:
        LOGGER.warning(f"⚠️ GitHub assets check failure for {url}: {r.status_code} {r.reason}")
        return "", []
    data = r.json()
    return data["tag_name"], [x["name"] for x in data["assets"]]  # tag, assets i.e. ['yolov8n.pt', 'yolov8s.pt', ...]

def attempt_download_asset(file, repo="ultralytics/assets", release="v8.2.0", **kwargs):
    """
    Attempt to download a file from GitHub release assets if it is not found locally. The function checks for the file
    locally first, then tries to download it from the specified GitHub repository release.

    Args:
        file (str | Path): The filename or file path to be downloaded.
        repo (str, optional): The GitHub repository in the format 'owner/repo'. Defaults to 'ultralytics/assets'.
        release (str, optional): The specific release version to be downloaded. Defaults to 'v8.2.0'.
        **kwargs (any): Additional keyword arguments for the download process.

    Returns:
        (str): The path to the downloaded file.

    Example:
        ```python
        file_path = attempt_download_asset('yolov8n.pt', repo='ultralytics/assets', release='latest')
        ```
    """
    from ultralytics.utils import SETTINGS  # scoped for circular import

    # YOLOv3/5u updates
    file = str(file)
    file = checks.check_yolov5u_filename(file)
    file = Path(file.strip().replace("'", ""))
    if file.exists():
        return str(file)
    elif (SETTINGS["weights_dir"] / file).exists():
        return str(SETTINGS["weights_dir"] / file)
    else:
        # URL specified
        name = Path(parse.unquote(str(file))).name  # decode '%2F' to '/' etc.
        download_url = f"https://github.com/{repo}/releases/download"
        if str(file).startswith(("http:/", "https:/")):  # download
            url = str(file).replace(":/", "://")  # Pathlib turns :// -> :/
            file = url2file(name)  # parse authentication https://url.com/file.txt?auth...
            if Path(file).is_file():
                LOGGER.info(f"Found {clean_url(url)} locally at {file}")  # file already exists
            else:
                safe_download(url=url, file=file, min_bytes=1e5, **kwargs)

        elif repo == GITHUB_ASSETS_REPO and name in GITHUB_ASSETS_NAMES:
            safe_download(url=f"{download_url}/{release}/{name}", file=file, min_bytes=1e5, **kwargs)

        else:
            tag, assets = get_github_assets(repo, release)
            if not assets:
                tag, assets = get_github_assets(repo)  # latest release
            if name in assets:
                safe_download(url=f"{download_url}/{tag}/{name}", file=file, min_bytes=1e5, **kwargs)

        return str(file)

def download(url, dir=Path.cwd(), unzip=True, delete=False, curl=False, threads=1, retry=3, exist_ok=False):
    """
    Downloads files from specified URLs to a given directory. Supports concurrent downloads if multiple threads are
    specified.

    Args:
        url (str | list): The URL or list of URLs of the files to be downloaded.
        dir (Path, optional): The directory where the files will be saved. Defaults to the current working directory.
        unzip (bool, optional): Flag to unzip the files after downloading. Defaults to True.
        delete (bool, optional): Flag to delete the zip files after extraction. Defaults to False.
        curl (bool, optional): Flag to use curl for downloading. Defaults to False.
        threads (int, optional): Number of threads to use for concurrent downloads. Defaults to 1.
        retry (int, optional): Number of retries in case of download failure. Defaults to 3.
        exist_ok (bool, optional): Whether to overwrite existing contents during unzipping. Defaults to False.

    Example:
        ```python
        download('https://ultralytics.com/assets/example.zip', dir='path/to/dir', unzip=True)
        ```
    """
    dir = Path(dir)
    dir.mkdir(parents=True, exist_ok=True)  # make directory
    if threads > 1:
        with ThreadPool(threads) as pool:
            pool.map(
                lambda x: safe_download(
                    url=x[0],
                    dir=x[1],
                    unzip=unzip,
                    delete=delete,
                    curl=curl,
                    retry=retry,
                    exist_ok=exist_ok,
                    progress=threads <= 1,
                ),
                zip(url, repeat(dir)),
            )
            pool.close()
            pool.join()
    else:
        for u in [url] if isinstance(url, (str, Path)) else url:
            safe_download(url=u, dir=dir, unzip=unzip, delete=delete, curl=curl, retry=retry, exist_ok=exist_ok)