How to use C++ struct in struct in Python

Question

I have to transfer the C++ code into Micro Python to Wipy platform. Currently, I've some problems with it, especially with accesing the variables from other structures

C++ code:

typedef struct {
    char id[100];
    int rssi;
} tag_info;

typedef struct {
    tag_info tag[20];
} tag_list;

typedef struct {
    int timestamp;
    tag_list tags;
    int heading;
    int airt;
} data_packet;

data_packet packet;

for (i = 0; i < total_amount_of_tags - 1; i++) {
            print_function("id", packet.tags.tag[i].id, destination); 
            print_function("rssi", packet.tags.tag[i].rssi, destination);
        }

My MicroPython code:

class tag_info:
    def __init__(self):
        self.id = ""
        self.rssi = 0

class tag_list:
    def __init__(self):
        self.tag = tag_info

class data_packet():
    def __init__(self):
        self.timestamp=0
        self.tags = tag_list
        self.heading=0
        self.airt=0

packet=data_packet()

for i in range(0, total_amount_of_tags -1)
    print_function('id',packet.tags.tag[i].id,destination)
    print_function("rssi", packet.tags.tag[i].rssi, destination);

The problem in my code that I cant access tag[i] and further variables. Should I use inheritance or namedTuple in this case. If i try to use namedTuple from collections import namedTuple the following error message occurs: no module called collections, so I would prefer to avoid that library if possible

Proper variant is namedtuple, but not namedTuple. Using this datatype is preferrable, there is no neccessary to build your own datatypes — Dmitry
– Dmitry, Commented Jan 9, 2019 at 13:47
To decide Import error - please provide python version and system info — Dmitry
– Dmitry, Commented Jan 9, 2019 at 13:48
for that project I use micropython on wipy 3.0 with the latest firmware upgrade — makar
– makar, Commented Jan 10, 2019 at 17:51

roeesha · Accepted Answer · 2019-01-09 13:47:31Z

3

In the following:

self.tag = tag_info

You are assigning a class to a variable. I assume you meant to do:

self.tag = tag_info()

but if I understand correctly this is supposed to be a list of tag_info, so you actually need is:

self.tag = [tag_info() for i in range(20)]

same goes for:

self.tags = tag_list()

answered Jan 9, 2019 at 13:47

roeesha

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James · Accepted Answer · 2019-01-09 13:50:32Z

2

This is a bit confusing as to what the expected behavior is supposed to be. But it looks like you need to create 20 instances of tag_info. Also you need to instantiate your instances using ().

class tag_info:
    def __init__(self):
        self.id = ""
        self.rssi = 0

class tag_list:
    def __init__(self):
        self.tag = [tag_info() for _ in range(20)]

class data_packet():
    def __init__(self):
        self.timestamp=0
        self.tags = tag_list()
        self.heading=0
        self.airt=0

answered Jan 9, 2019 at 13:50

James

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