Gr.sig_source_f - where is it

I do my first steps in GnuRAdio framework and i try to understand some
basics.

For example i add the following line

print(src0)

in the dial_tone.py to see what i take. But i don’t understand its
output, and i try to find the definition of gr.sig_source_f.

I use the command

find ./gnuradio -name sig_source_f.py

to locate the file, but i don’t find anything. Where can i find the code
of gr.sig_source_f?

(Also i’m new in python)