Python breakpoints in Vim (Vimscript)

I recently decided that putting strategically placed print statements scattered about my python programs to debug was getting to be a little messy.

I had thought to try out other debugging plugins I found online, but thought I would give writing my own simple breakpoint plugin a shot.

I know of python's pdb module, but my goal was to minimize the amount that I had to type to debug my programs.

Only a few keybinds are mapped:

Normal mode:

• <leader>b — Toggle breakpoint for the current line
• <leader>B — Run debugger in a new tmux split

Visual Mode:

• <leader>b — Toggle breakpoint for the selected lines

This has only been tested on Linux. The only requirement is tmux

" Define breakpoint highlight color and mark in number column
hi Breakpoint ctermfg=1 ctermbg=NONE
sign define Breakpoint text=● texthl=Breakpoint

" Map of lines that have breakpoints
let b:breakpoints = {}

function ToggleBreakpoint(lnum)
    let is_breakpoint = get(b:breakpoints, a:lnum, 0)

    if is_breakpoint
        " Remove the line number in breakpoints and unplace the mark
        call remove(b:breakpoints, a:lnum)
        exe ":sign unplace"
    else
        " Add the line number in breakpoints and place the mark
        let b:breakpoints[a:lnum] = 1
        exe ":sign place 2 line=" . a:lnum . " name=Breakpoint file=" . expand("%:p")
    endif
endfunction

function BreakpointIndentation(lnum)
    " Get the line's current indentation level and first character
    let indent_count = indent(a:lnum)
    let curline = getline(a:lnum)
    let firstChar = curline[0]

    " Build the indentation to use for the breakpoint
    if firstChar == "\t"
        " Handle user defined `tabstop` variable
        return repeat(firstChar, indent_count / &tabstop)
    else if firstChar == " "
        return repeat(firstChar, indent_count)
    else
        return ""
    endif
endfunction

function RunPDB()
    let lnum = 1
    let num_lines = line("$")

    " The lines to write to the temporary file
    " Start out by importing pdb
    let lines = ["import pdb"]

    " Iterate over each line in the current buffer
    while lnum <= num_lines
        let is_breakpoint = get(b:breakpoints, lnum, 0)

        " If the line is a breakpoint, add `pdb.set_trace` before that line
        if is_breakpoint
            let indentation = BreakpointIndentation(lnum)
            let breakpoint_line = "pdb.set_trace()"
            if indentation != ""
                let breakpoint_line = indentation . breakpoint_line
            endif
            call add(lines, breakpoint_line)
        endif

        call add(lines, getline(lnum))
        let lnum += 1
    endwhile

    " Create a new temporary file with the contents of `lines`
    let tmpfile = tempname()
    call writefile(lines, tmpfile)

    " Make a new vertical tmux split and run the temporary file with python
    silent exe "!tmux split-pane -v"
    silent exe "!tmux send-keys 'python " . tmpfile . "' Enter"

endfunction

nnoremap <leader>b :call ToggleBreakpoint(line("."))<CR>
vnoremap <leader>b :call ToggleBreakpoint(line("."))<CR>
nnoremap <leader>B :call RunPDB()<CR>

This is my first attempt to write anything particularly useful in vimscript.

Are there any sections that can be improved upon?