[SciPy-user] NumPy Newcomer Questions: Reading Data Stream & Building Array

Rich Shepard rshepard at appl-ecosys.com
Fri Sep 8 18:35:24 CDT 2006


On Sat, 9 Sep 2006, Johannes Loehnert wrote:

> Understood now. But you cannot store strings and floats in an array
> simultaneously.

Johannes,

   I understand. I was thinking of lists, I guess. This is not a problem
because I can store a numeric code (1, 2, 3) for each of the two strings and
translate them later in the program. They're there for selecting rows.
Originally I was going to put the incoming data into a SQLite3 database
table, then extract the values using SQL 'select from ... where ...'
statements, but I thought that direct application of python datatypes would
be more efficient.

> Not sure about string.split(), I don't think this is useful (would split
> into 1-byte chars iirc). You can you use a list comprehension for the data
> part, like this:

   One-byte chars are exactly what I want. That's what is coming from the
scanner, in bit-mapped format. What the scanner folks call a column we see
as a row on the form. Each 'row' (as we look at the form in portrait
orientation) has 12 positions, each with a bit value. There are two bytes
encoded there. I'm using the DATA_MAP_ dictionaries to translate from the
transmitted bytes to values meaningful to the application.

> line = read_data()
> mapped_vals = [DATA_MAP_7[i:i+2] for i in range(2*7, 2*35)]

   DATA_MAP is a dictionary; can I find keys by slicing? If so, it would be
[i:i+1] from bytes 12-67.

> although I admit it is no very pretty solution. Maybe somebody has a better
> idea.

   You are helping me, but what I'm trying to do is beyond what all my
introductory references cover, and I'm not finding clearly presented
solutions using Google.

> BTW, while having a closer look to your code I noticed that at line 72
> = ("line ser.readline") there is a pair of brackets missing. Here is one
> free of charge: ()
> ;-)

   Thank you. I caught that earlier today and fixed it.

Rich

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