sidereal.py: Internal maintenance specification

A service routine, this function removes a floating-point number from the head of s.

# - - -   p a r s e F l o a t

def parseFloat ( s, message ):
    """Parse a floating-point number at the front of s.

      [ (s is a string) and
        (message is a string describing what is expected) ->
          if s begins with a floating-point number ->
            return (x, tail) where x is the number as type float
            and tail is the part of s after the match
          else -> raise SyntaxError, "Expecting (message)" ]
    """

We use the precompiled regular expression from Section 8.6, “FLOAT_PAT: Regular expression for a floating-point number” to match the number.

    #-- 1 --
    # [ if the front of s matches FLOAT_PAT ->
    #     m  :=  a Match object describing the match
    #   else -> raise SyntaxError ]
    rawFloat, tail  =  parseRe ( s, FLOAT_PAT, message )

The matching string is available as m.group(). The position just after the match is available as m.end().

    #-- 2 --
    return  (float(rawFloat), tail)