How to put partial command in command bar?

Question

I am trying to do something like this, from a function:

nmap <F5> :!python %

Pressing F5 in this case causes the command :!python % to be left in the command line. This is preferred for me, because occasionally I may want to add extra command arguments or stuff to the end of the command.

However, I'm not sure how to create this behavior from a vim function. The execute() function simply executes the command directly, with no chance of editing, while the normal command doesn't seem to work.

nmap <F5> :call MyDebugFunction()<cr>

function! MyDebugFunction()
  " This just executes right away with no chance of editing
  execute("python %")
  " Neither of these work
  normal! :!python %
  execute "normal! :!python%"
endfunction

Answer 1

This is one of the very rare cases in which feedkeys() is actually called for. Doing :call feedkeys(':!python %') should work, since feedkeys puts stuff directly on vim's input buffer.

Answer 2

while the normal command doesn't seem to work

normal must always return to Normal. It is considered normal in Vim.

I am trying to do something like this, from a function

Not really useful for this simple example, but, in general, there are many situations one may want it. Simply make use of :h map-expr (or, alternatively, the expression register), like this:

nnoremap <expr>F5 MyFunction()

function! MyFunction() abort
    " foo, bar, baz..
    return ":!python %"
endfunction