Repository: yt-dlp/yt-dlp
File: yt_dlp/utils.py (Python)

Code before:
    Each of the provided `paths` is tested and the first producing a valid result will be returned.
    The next path will also be tested if the path branched but no results could be found.
    Supported values for traversal are `Mapping`, `Sequence` and `re.Match`.
    Unhelpful values (`{}`, `None`) are treated as the absence of a value and discarded.

    The paths will be wrapped in `variadic`, so that `'key'` is conveniently the same as `('key', )`.

    The keys in the path can be one of:
        - `None`:           Return the current object.
        - `set`:            Requires the only item in the set to be a type or function,
                            like `{type}`/`{func}`. If a `type`, returns only values
                            of this type. If a function, returns `func(obj)`.
        - `str`/`int`:      Return `obj[key]`. For `re.Match`, return `obj.group(key)`.
        - `slice`:          Branch out and return all values in `obj[key]`.
        - `Ellipsis`:       Branch out and return a list of all values.
        - `tuple`/`list`:   Branch out and return a list of all matching values.
                            Read as: `[traverse_obj(obj, branch) for branch in branches]`.
        - `function`:       Branch out and return values filtered by the function.
                            Read as: `[value for key, value in obj if function(key, value)]`.
                            For `Sequence`s, `key` is the index of the value.
                            For `re.Match`es, `key` is the group number (0 = full match)
                            as well as additionally any group names, if given.
        - `dict`            Transform the current object and return a matching dict.
                            Read as: `{key: traverse_obj(obj, path) for key, path in dct.items()}`.

        `tuple`, `list`, and `dict` all support nested paths and branches.

    @params paths           Paths which to traverse by.
    @param default          Value to return if the paths do not match.
                            If the last key in the path is a `dict`, it will apply to each value inside
                            the dict instead, depth first. Try to avoid if using nested `dict` keys.
    @param expected_type    If a `type`, only accept final values of this type.
                            If any other callable, try to call the function on each result.
                            If the last key in the path is a `dict`, it will apply to each value inside
                            the dict instead, recursively. This does respect branching paths.
    @param get_all          If `False`, return the first matching result, otherwise all matching ones.
    @param casesense        If `False`, consider string dictionary keys as case insensitive.

    The following are only meant to be used by YoutubeDL.prepare_outtmpl and are not part of the API

    @param is_user_input    Whether the keys are generated from user input.
                            If `True` strings get converted to `int`/`slice` if needed.
    @param traverse_string  Whether to traverse into objects as strings.
                            If `True`, any non-compatible object will first be
                            converted into a string and then traversed into.
                            The return value of that path will be a string instead,
                            not respecting any further branching.


    @returns                The result of the object traversal.
                            If successful, `get_all=True`, and the path branches at least once,

Review comment (suggestion):
As `Iterable` has no `index()`, I chose:
```
                            For `Iterable`s, `key` is the enumeration count of the value.
```

Code after:
    Safely traverse nested `dict`s and `Iterable`s

    >>> obj = [{}, {"key": "value"}]
    >>> traverse_obj(obj, (1, "key"))
    "value"

    Each of the provided `paths` is tested and the first producing a valid result will be returned.
    The next path will also be tested if the path branched but no results could be found.
    Supported values for traversal are `Mapping`, `Iterable` and `re.Match`.
    Unhelpful values (`{}`, `None`) are treated as the absence of a value and discarded.

    The paths will be wrapped in `variadic`, so that `'key'` is conveniently the same as `('key', )`.

    The keys in the path can be one of:
        - `None`:           Return the current object.
        - `set`:            Requires the only item in the set to be a type or function,
                            like `{type}`/`{func}`. If a `type`, returns only values
                            of this type. If a function, returns `func(obj)`.
        - `str`/`int`:      Return `obj[key]`. For `re.Match`, return `obj.group(key)`.
        - `slice`:          Branch out and return all values in `obj[key]`.
        - `Ellipsis`:       Branch out and return a list of all values.
        - `tuple`/`list`:   Branch out and return a list of all matching values.
                            Read as: `[traverse_obj(obj, branch) for branch in branches]`.
        - `function`:       Branch out and return values filtered by the function.
                            Read as: `[value for key, value in obj if function(key, value)]`.
                            For `Iterable`s, `key` is the index of the value.
                            For `re.Match`es, `key` is the group number (0 = full match)
                            as well as additionally any group names, if given.
        - `dict`            Transform the current object and return a matching dict.
                            Read as: `{key: traverse_obj(obj, path) for key, path in dct.items()}`.

        `tuple`, `list`, and `dict` all support nested paths and branches.

    @params paths           Paths which to traverse by.
    @param default          Value to return if the paths do not match.
                            If the last key in the path is a `dict`, it will apply to each value inside
                            the dict instead, depth first. Try to avoid if using nested `dict` keys.
    @param expected_type    If a `type`, only accept final values of this type.
                            If any other callable, try to call the function on each result.
                            If the last key in the path is a `dict`, it will apply to each value inside
                            the dict instead, recursively. This does respect branching paths.
    @param get_all          If `False`, return the first matching result, otherwise all matching ones.
    @param casesense        If `False`, consider string dictionary keys as case insensitive.

    The following are only meant to be used by YoutubeDL.prepare_outtmpl and are not part of the API

    @param is_user_input    Whether the keys are generated from user input.
                            If `True` strings get converted to `int`/`slice` if needed.
    @param traverse_string  Whether to traverse into objects as strings.
                            If `True`, any non-compatible object will first be
                            converted into a string and then traversed into.