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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 convert_string(string, chars=None):
 """Remove certain characters from a string."""

    if chars is None:
        chars = [',', '.', '-', '/', ':', '  ']

    for ch in chars:
        if ch in string:
            string = string.replace(ch, ' ')
    return string