Pasting from vim to an ipython terminal

Question

I have an open ipython terminal open, and I'd like to paste the visual selection to it, with prepending "%cpaste" and appending "--"

This is what I came up with

function! VisualSelection()
    if mode()=="v"
        let [line_start, column_start] = getpos("v")[1:2]
        let [line_end, column_end] = getpos(".")[1:2]
    else
        let [line_start, column_start] = getpos("'<")[1:2]
        let [line_end, column_end] = getpos("'>")[1:2]
    end
    if (line2byte(line_start)+column_start) > (line2byte(line_end)+column_end)
        let [line_start, column_start, line_end, column_end] =
        \   [line_end, column_end, line_start, column_start]
    end
    let lines = getline(line_start, line_end)
    if len(lines) == 0
            return get_line(line('.'))                                                                                                                                                                               endif
    let lines[-1] = lines[-1][: column_end - 1]
    let lines[0] = lines[0][column_start - 1:]
    return join(lines, "\n")
endfunction

vnoremap <silent> <F7> :call term_sendkeys(term_list()[0], "%cpaste\n".VisualSelection())."\n--\n")<cr>

Unfortunately, for some reason the string "cpaste" gets sent multiple times, and the rest is sent after that.

Any ideas what could be the problem ?