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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 _realValue_to_float(value_str):
 """ Convert a value string that conforms to DSP0004 `realValue`, into the corresponding float and return it. The special values 'INF', '-INF', and 'NAN' are supported. Note that the Python `float()` function supports a superset of input formats compared to the `realValue` definition in DSP0004. For example, "1." is allowed for `float()` but not for `realValue`. In addition, it has the same support for Unicode decimal digits as `int()`. Therefore, the match patterns explicitly check for US-ASCII digits, and the `float()` function should never raise `ValueError`. Returns None if the value string does not conform to `realValue`. """

    if REAL_VALUE.match(value_str):
        value = float(value_str)
    else:
        value = None
    return value