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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 select_regexp_char(char):
 """ Select correct regex depending the char """

    regexp = '{}'.format(char)

    if not isinstance(char, str) and not isinstance(char, int):
        regexp = ''

    if isinstance(char, str) and not char.isalpha() and not char.isdigit():
        regexp = r"\{}".format(char)

    return regexp