PYTHON

print a number with commas as thousands separator

Example: 10000000.2345 -> '1,000,000.2345'
function numberWithCommas(x) {
    var parts = x.toString().split(".");
    parts[0] = parts[0].replace(/B(?=(d{3})+(?!d))/g, ",");
    return parts.join(".");
}

using comma as the thousand separator

>>> '{:,}'.format(1234567890)
'1,234,567,890'