Strange issues with python-dap

[zephod77]

Here is my nvim-dap.lua file:

return {
    "mfussenegger/nvim-dap",
    dependencies = {
        "rcarriga/nvim-dap-ui",         -- creates debugger UI
        "nvim-neotest/nvim-nio",        -- required by dap-ui
        "mfussenegger/nvim-dap-python", -- python debugger
    },
    config = function()
        local dap = require('dap')
        local dapui = require("dapui")

        require('dap-python').setup()
        dap.configurations.python = {
            {
                type = 'python',
                request = 'launch',
                name = "Launch file",
                program = "${file}",
                pythonPath = function() return '/usr/bin/python' end,
            },
        }

        dap.listeners.before.attach.dapui_config = function()
            dapui.open()
        end
        dap.listeners.before.launch.dapui_config = function()
            dapui.open()
        end
        dap.listeners.before.event_terminated.dapui_config = function()
            dapui.close()
        end
        dap.listeners.before.event_exited.dapui_config = function()
            dapui.close()
        end

        vim.keymap.set("n", "<leader>dc", dap.continue, {})
        vim.keymap.set('n', '<leader>dt', dap.toggle_breakpoint, {})
    end,
}

I also have which-key configured. If I open a python file and look at the key_bindings, <Leader>dc
and <Leader>dt are not defined and they don't work (ie its not a which-key problem)
If I issue, this command in the python file:
:lua require'dap'.set_log_level('INFO')
then which-key does show the mappings. <Leader>dt appears to work and a 'B' shows up in the margin. <Leader>dc kind of works in that an arrow appears in the margin replacing the B but none of the UI elements open as expected.

When I repeated the exercise I got this crash:

Lazy shows that nvim-dap, nvim-dap-python, nvim-dap-ui and nvim-io are installed but not loaded.
Mason shows that debugpy is installed.

This is on an old Ubuntu 20.04 machine and I have both python2 and python3 installed. /usr/bin/python is a symbolic link to /usr/bin/python3.

Can anyone explain what is happening and how I can get the dap-ui to show up?

Steve

[zephod77]

Well, I've figured out part of the answer.
I needed to add
dapui.setup()
to my configuration. That gets the UI windows to appear once I have run the set_log_level() command.
It appears that nvim-dap is not loaded/running until it gets kick-started with a manual command. I'm guessing that I'm missing something else from my configuration.