Recently a DCF77 receiver and decoder program based on Python and GNU Radio has been uploaded to GitHub
https://github.com/henningM1r/gr_DCF77_Receiver
by henningM1r. It includes a simulator written in Python so you can simulate your own DCF77 signal for testing the receiver too.

Currently the decoder has been tested to work with an Airspy HF+ Discovery SDR, but it should work with any SDR capable of receiver 77.5 kHz if the GNU Radio source block is changed out.