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

Code before:
                (Actions.REPLACE, field, search, replace)
        """
        if action not in cls.Actions:
            raise ValueError(f'{action!r} is not a valid action')
        action(cls, *data)  # So this can raise error to validate

    @staticmethod
    def field_to_template(tmpl):
        if re.match(r'[a-zA-Z_]+$', tmpl):
            return f'%({tmpl})s'

        from ..YoutubeDL import YoutubeDL
        err = YoutubeDL.validate_outtmpl(tmpl)
        if err:
            raise err
        return tmpl

    @staticmethod
    def format_to_regex(fmt):
        r"""
        Converts a string like
           '%(title)s - %(artist)s'
        to a regex like
           '(?P<title>.+)\ \-\ (?P<artist>.+)'
        """
        ALLOWABLE_GROUP_NAME_RE = r'[a-zA-Z](?:[a-zA-Z0-9_]+)?'
        if not re.search(rf'%\({ALLOWABLE_GROUP_NAME_RE}\)s', fmt):
            if re.fullmatch(ALLOWABLE_GROUP_NAME_RE, fmt):
                # convert a single field name into regex pattern that matches the entire input
                return rf'(?s)(?P<{fmt}>.+)'
            return fmt
        lastpos = 0
        regex = ''
        # replace %(..)s with regex group and escape other string parts
        for match in re.finditer(rf'%\(({ALLOWABLE_GROUP_NAME_RE})\)s', fmt):
            regex += re.escape(fmt[lastpos:match.start()])
            regex += rf'(?P<{match.group(1)}>.+)'
            lastpos = match.end()
        if lastpos < len(fmt):
            regex += re.escape(fmt[lastpos:])
        return regex

    def run(self, info):
        for f in self._actions:
            f(info)
        return [], info

    @function_with_repr
    def interpretter(self, inp, out):
        def f(info):
            data_to_parse = self._downloader.evaluate_outtmpl(template, info)

Review comment (suggestion):
```suggestion
        ALLOWABLE_GROUP_NAME_RE = r'[a-zA-Z][a-zA-Z0-9_]*'
```

Code after:
                (Actions.REPLACE, field, search, replace)
        """
        if action not in cls.Actions:
            raise ValueError(f'{action!r} is not a valid action')
        action(cls, *data)  # So this can raise error to validate

    @staticmethod
    def field_to_template(tmpl):
        if re.match(r'[a-zA-Z_]+$', tmpl):
            return f'%({tmpl})s'

        from ..YoutubeDL import YoutubeDL
        err = YoutubeDL.validate_outtmpl(tmpl)
        if err:
            raise err
        return tmpl

    @staticmethod
    def format_to_regex(fmt):
        r"""
        Converts a string like
           '%(title)s - %(artist)s'
        to a regex like
           '(?P<title>.+)\ \-\ (?P<artist>.+)'
        """
        if re.fullmatch(r'\w+', fmt):
            # convert a single field name into regex pattern that matches the entire input
            return rf'(?s)(?P<{fmt}>.+)'
        if not re.search(r'%\(\w+\)s', fmt):
            return fmt
        lastpos = 0
        regex = ''
        # replace %(..)s with regex group and escape other string parts
        for match in re.finditer(r'%\((\w+)\)s', fmt):
            regex += re.escape(fmt[lastpos:match.start()])
            regex += rf'(?P<{match.group(1)}>.+)'
            lastpos = match.end()
        if lastpos < len(fmt):
            regex += re.escape(fmt[lastpos:])
        return regex

    def run(self, info):
        for f in self._actions:
            f(info)
        return [], info

    @function_with_repr
    def interpretter(self, inp, out):
        def f(info):
            data_to_parse = self._downloader.evaluate_outtmpl(template, info)
            self.write_debug(f'Searching for {out_re.pattern!r} in {template!r}')