[Python] How to implement a callback using PyCall?

I would like to access a Python package in Ruby using PyCall.

The non-blocking function in the Python code below activates a callback.

Could you help me implement the callback?

#!/usr/bin/env python
# start_reading.py
import time
import mercury

def found(tag):
print(tag.epc.decode()) # Check check
# print(tags[1].epc.decode())

reader = mercury.Reader("tmr:///dev/ttyUSB0")

reader.start_reading(found, on_time=250, off_time=0)
time.sleep(0.5)
reader.stop_reading()


Output start_reading.py:

b'001853000000000000000012'
b'34155CACB400000000000125'
b'34155CACB400000000000125'
b'34155CACB400000000000125'
b'001853000000000000000012'
b'34155CACB400000000000125'
b'001853000000000000000012'
b'34155CACB400000000000125'
b'34155CACB400000000000125'


This pertains an api for ThingMagic RFID readers, which is a Python wrapper for the original api written in C.

From the docs:

reader.start_reading(callback, on_time=250, off_time=0)

Starts asynchronous reading. It returns immediately and begins a sequence of reads or a continuous read. The results are passed to the callback. The reads are repeated until the reader.stop_reading() method is called

• callback(TagReadData) will be invoked for every tag detected
• on_time sets the duration, in milliseconds, for the reader to be actively querying
• off_time duration, in milliseconds, for the reader to be quiet while querying

​

As follows the parts I got working using a single read function. First the Python code, then Ruby.

#!/usr/bin/env python
# read.py
import mercury
reader = mercury.Reader("tmr:///dev/ttyUSB0")

data = reader.read()
print(data)
print(f"type: {type(data)}")


Output read.py:

[EPC(b'34155CACB400000000000125'), EPC(b'001853000000000000000012')]
type: <class 'list'>


#!/usr/bin/env ruby
# read.rb
require 'pycall/import'
include PyCall::Import
pyimport :mercury

reader = mercury.Reader.new("tmr:///dev/ttyUSB0")

python_data = reader.read()
puts "python_data: #{python_data}"
puts "python class: #{python_data.class}"
puts ""
ruby_data = python_data.to_ary
puts "ruby_data: #{ruby_data}"
puts "ruby class: #{ruby_data.class}"


Output read.rb:

python_data: [EPC(b'34155CACB400000000000125'), EPC(b'001853000000000000000012')]
python class: <class 'list'>

ruby_data: [EPC(b'34155CACB400000000000125'), EPC(b'001853000000000000000012')]
ruby class: Array


The above works, as you can see.

The solution for the callback should be an improvement upon the following code.

#!/usr/bin/env ruby
# start_reading.rb
require 'pycall/import'
include PyCall::Import
pyimport :mercury

def found(tag)
puts tag.epc
end

reader = mercury.Reader.new("tmr:///dev/ttyUSB0")

reader.start_reading(found, on_time=250, off_time=0) # What should I do here?
sleep(0.5)
reader.stop_reading()


Current output start_reading.rb

start_reading.rb:7:in `found': wrong number of arguments (given 0, expected 1) (ArgumentError)
from start_reading.rb:14:in `<main>'

Continue reading...