python-lists.py

# Dictionary to store stream responses in
responses = {
    "123": [],
    "456": [],
}

# Dummy stream
port_123_stream = ["I am a line", "I like cake", "Turtles too"]
port_456_stream = ["Some other line", "Pizza party", "Puppy power"]

# Dummy subscription to the port's stream
for line in port_123_stream:
    port = "123"
    responses[port].append(line)

# Dummy subscription to another port's stream.
for line in port_456_stream:
    port = "456"
    responses[port].append(line)

# Should output something like
# {'123': ['I am a line', 'I like cake', 'Turtles too'], '456': ['Some other line', 'Pizza party', 'Puppy power']}
print(responses)