Multiway Branching

Fredrik Lundh fredrik at pythonware.com
Sun Jan 8 20:31:49 CET 2006


rshepard at appl-ecosys.com wrote:

>   I need to look at two-byte pairs coming from a machine, and interpret the
> meaning based on the relative values of the two bytes. In C I'd use a switch
> statement. Python doesn't have such a branching statement. I have 21
> comparisons to make, and that many if/elif/else statements is clunky and
> inefficient. Since these data are coming from an OMR scanner at 9600 bps (or
> faster if I can reset it programmatically to 38K over the serial cable), I
> want a fast algorithm.
>
>   The data are of the form:
>
>   if byte1 == 32 and byte2 == 32:
> row_value = 0
>   elif byte1 == 36 and byte2 == 32:
> row_value = "natural"
>    ...
>   elif byte1 == 32 and byte2 == 1:
> row_value = 5
>   elif byte1 == 66 and byte2 == 32:
> row_value = 0.167
>
>   There are two rows where the marked response equates to a string and 28
> rows where the marked response equates to an integer (1-9) or float of
> defined values.

DATA_MAP = {
    chr(32)+chr(32): 0,
    chr(36)+chr(32): "natural",
    ...
    chr(32)+chr(1): 5,
    chr(66)+chr(32): 0.167,
}

...

row_value = DATA_MAP[source.read(2)]

# or: row_value = DATA_MAP.get(source.read(2), DEFAULT)

</F>






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