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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 figure_naming(pretitle='', posttitle='', prefile='', postfile=''):
 """ Helper function to define the strings that handle pre-post conventions for viewing - plotting title and saving options. Args: pretitle(str):
 String to include before the general title of the figure. posttitle(str):
 String to include after the general title of the figure. prefile(str):
 String to include before the general filename of the figure. postfile(str):
 String to include after the general filename of the figure. Returns: str: String to include in the figure name and title, in a suitable form. """

    if pretitle:
        pretitle = "%s -- " % pretitle

    if posttitle:
        posttitle = " -- %s" % posttitle

    if prefile:
        prefile = "%s_" % prefile

    if postfile:
        postfile = "_%s" % postfile

    return pretitle, posttitle, prefile, postfile