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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 _cellrepr(value, allow_formulas):
 """ Get a string representation of dataframe value. :param :value: the value to represent :param :allow_formulas: if True, allow values starting with '=' to be interpreted as formulas; otherwise, escape them with an apostrophe to avoid formula interpretation. """

    if pd.isnull(value) is True:
        return ""
    if isinstance(value, float):
        value = repr(value)
    else:
        value = str(value)
    if (not allow_formulas) and value.startswith('='):
        value = "'%s" % value
    return value