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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 glob_handler(extension, folder=None, identifier=None):
 """Return a list of all files matching specified inputs. Parameters extension : string File extension. folder : string (optional) Folder to search within. Default is None (current working directory). identifier : string Unique identifier. Default is None. Returns ------- list of strings Full path of matching files. """

    filepaths = []
    if folder:
        # comment out [ and ]...
        folder = folder.replace("[", "?")
        folder = folder.replace("]", "*")
        folder = folder.replace("?", "[[]")
        folder = folder.replace("*", "[]]")
        glob_str = os.path.join(folder, "*" + extension)
    else:
        glob_str = "*" + extension + "*"
    for filepath in glob.glob(glob_str):
        if identifier:
            if identifier in filepath:
                filepaths.append(filepath)
        else:
            filepaths.append(filepath)
    return filepaths