Block not found in module although it is there

Dear all,

my problem concerns GNU Radio version 3.8 from the maintenance branch
but it is probably not limited to this version.

I would like to try to adapt the block "ofdm_synchronization" that
Federico Larrocca and others have developed for ISDB-T so that it can be
used for DVB-T. For this purpose I have created the module "gr-dl5eu"
that contains a block called "dvbt_ofdm_synchronization".

As long as the block only passes data from the input to the output
everything is ok. But when I start to add code to the constructor, the
block dvbt_ofdm_synchronization is no longer found in gr-dl5eu when I
run the flow graph.

My constructor looks like this:

dvbt_ofdm_synchronization_impl::dvbt_ofdm_synchronization_impl(int mode,
int cp_length, bool interpolate
    : gr::block("dvbt_ofdm_synchronization",
        gr::io_signature::make(1, 1, sizeof(gr_complex)),
        gr::io_signature::make(1, 1, sizeof(gr_complex)))
{
}

Everything is fine, the block copies data from input to output.

But when I add the variable "d_fft_calculator" to the private section of
the object and the following line just before the opening brace of the
constructor: "    , d_fft_calculator(gr::fft::fft_complex(pow(2.0,
10+mode), true, 1))", I get an error message when I run the flow graph:
"AttributeError: module 'dl5eu' has no attribute
'dvbt_ofdm_synchronization'"

The complete messages are below.

<<< Welcome to GNU Radio Companion v3.8.2.0-113-g729d5a98 >>>
Block paths:
/usr/share/gnuradio/grc/blocks
Loading: "/home/ralfg/gnuradio/dvbt_rx_udp.grc"
>>> Done
Generating: '/home/ralfg/gnuradio/dvbt_rx_udp.py'
Executing: /usr/bin/python3 -u /home/ralfg/gnuradio/dvbt_rx_udp.py

qt5ct: using qt5ct plugin
gr-osmosdr 0.2.0.0 (0.2.0) gnuradio v3.8.2.0-113-g729d5a98
built-in source types: file rtl rtl_tcp rfspace redpitaya
Using device #0 Realtek RTL2838UHIDIR SN: 00000001
Found Rafael Micro R820T tuner
Setting rtl clock to 28800000 Hz.
Setting tuner clock to 28800000 Hz.
[R82XX] PLL not locked!
Exact sample rate is: 1142857,021756 Hz
[R82XX] PLL not locked!
Traceback (most recent call last):
File "/home/ralfg/gnuradio/dvbt_rx_udp.py", line 404, in <module>
main()
File "/home/ralfg/gnuradio/dvbt_rx_udp.py", line 380, in main
tb = top_block_cls()
File "/home/ralfg/gnuradio/dvbt_rx_udp.py", line 272, in __init__
self.dl5eu_dvbt_ofdm_synchronization_0 =
dl5eu.dvbt_ofdm_synchronization(1, 0.125, True)
AttributeError: module 'dl5eu' has no attribute 'dvbt_ofdm_synchronization'
>>> Done (return code 1)

In the original code the initialization of "d_fft_calculator" the
initializatiion is done this way. I have the same problem when I change
d_fft_calculator to a pointer type and initialize it with "new" inside
of the constructor.

Can anybody give me a hint what is happening here? Is there something
missing in the .yml file? I have got the impression that C++ and GNU
Radio are indeed not made for beginners :-(

Thank you very much for your help!

Kind regards,

Ralf