You cannot access a tuple element with a string key. At some point the
options object is of a different class that
defines the indexing operator, or more likely, is actually a dictionary.
On 11/1/2021 12:30 PM, Helge Kruse wrote:
Hello,
I am not an experienced Python programmer. So I’d like to ask some
detail to the syntax I found in sigrok protocol decoders.
I wonder about the syntax or probably syntactic sugar in the
libsigrokdecode library. The sigrok protocol decoder API
(https://www.sigrok.org/wiki/Protocol_decoder_API) includes the
attribute “options” as a tuple consisting of dictionaries. The decoder
code itself reads the current options value with a “string index” like
in the UART decoder:
self.bw = (self.options['data_bits'] + 7) // 8
I want to run my decoder in a plain Python environment to make some
tests. Instead of deriving from “srd.Decoder” I can write the decoder
class like this:
class Decoder:
options = ( {'id': 'baudrate', 'desc': 'Baud rate', 'default': 115200}, )
def __init__(self):
pass
def start(self):
if options['baudrate'] == 9600:
pass
# test the class
if __name__ == "__main__":
d = Decoder()
d.start()
If I instantiate the class I get an exception for the first line in
the start method: “tuple indices must be integer or slices, not str”.
What is the magic behind the libsigrok implementation, that allows to
use a string to access a specific options value? Is there some Python
magic that helps to make the start method running in a plain Python
environment?
Best regards,
Helge
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