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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _iter_lexerclasses(plugins=True):
 """Return an iterator over all lexer classes."""

    for key in sorted(LEXERS):
        module_name, name = LEXERS[key][:2]
        if name not in _lexer_cache:
            _load_lexers(module_name)
        yield _lexer_cache[name]
    if plugins:
        for lexer in find_plugin_lexers():
            yield lexer