calculating distance

[Mr. Sakos the 3rd]

Hello,

I'm quite new to the Neo 6M GPS module and this library, but in my project I want to get an action, after calculating the distance (in m) from two different positions. Normally to get the latitude and longitude it would be something like that:

if newdata[0:6] == "$GPRMC":
module_data = pynmea2.parse(newdata)
lat=module_data.latitude
lng=module_data.longitude

So how to keep one point and measure a second one for subtract them to the distance in meters?

Thanks