[Django]-Download a text/csv file from django app that populates HTML table from a database query

In fact you are requesting the same set of data from your site. The only thing changing is the format. So normally you just want to request the same page with a GET parameter like ?format=csv. So your view function would look like this:

def from_samrun(request):    
    if request.GET:
        lab_query = request.GET['lab_number']
        var_list = VarSamRun.objects.filter(sample=lab_query)
        if request.GET['format'] == 'csv':
            response = HttpResponse('')
            response['Content-Disposition'] = 'attachment; filename=file.csv'   
            writer = csv.writer(response, dialect=csv.excel)
            writer.writerow(some_random_data_list)
            return response

        if var_list:
            return render(request, 'results/varlist.html', {'var_list': var_list,'lab_query':lab_query})
        else:
            return render(request, 'results/varlist.html', {'query': [sam_query]})
    else:
        return render(request, 'results/varlist.html' {'error': 'Error'})

And your template:

<form method='GET'>
    <input type='hidden' name='format' value='csv'>
    <input type='hidden' name='lab_query' value={{lab_query}}>
    <input type='submit'>
</form>