Re: [Discuss-gnuradio] Python Tutorial for MAC OS 10.12

[Michael Dickens]

Hi Luis Felipe - So section 3.1.5 is meant to show you some of the functionality of GRC and Python scripting. GRC is used as the primary means to create the flowgraph visually, and then to generate a Python script that can be executed. In this specific case, the tutorial is asking you to also edit the generated Python to show alternative functionality -- editing lines 74-80 roughly. The resulting lines should read like those found after the text "Thus we can go back and modify our probe function with the if-else statement to give power to our friend.". Note that the tutorial authors also made a copy of the generated Python script ... original is "if_else.py", and they copy it to "if_else_mod.py". I'd recommend doing so, to avoid overwriting from within GRC.

Yet another item to notice is that if your file "if_else_mod.py" reads like that found immediately after the text "Full code copied below:", then it will rarely execute cleanly (when running via "python if_else_mod.py" or the like; I'd actually recommend using "python2.7 if_else_mod.py" on Mac OS X, just to be clear). The error will read something like:

{{{

% python2.7 /tmp/if_else_mod.py

Exception in thread Thread-1:

Traceback (most recent call last):

  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 801, in __bootstrap_inner

    self.run()

  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 754, in run

    self.__target(*self.__args, **self.__kwargs)

  File "/tmp/if_else_mod.py", line 81, in _variable_function_probe_0_probe

    self.set_ampl(.3)

  File "/tmp/if_else_mod.py", line 177, in set_ampl

    self.analog_sig_source_x_1.set_amplitude(self.ampl)

  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/gnuradio/gr/hier_block2.py", line 92, in __getattr__

    return getattr(self._impl, name)

AttributeError: 'top_block_sptr' object has no attribute 'analog_sig_source_x_1'

}}}

The reason for the error is the changes made for this tutorial result in a variable (self.analog_sig_source_x_1) being accessed before it is created. A fix is to move the section of code with:

{{{

        def _variable_function_probe_0_probe():

            [snip]

         _variable_function_probe_0_thread = threading.Thread(target=_variable_function_probe_0_probe)

         _variable_function_probe_0_thread.daemon = True

         _variable_function_probe_0_thread.start()

}}}

to just before the text "# QT sink close method reimplementation" and at the same indentation level. The error comes about because the thread is started (the last line), and the thread starts executing & then calls "set_ampl" which in turn references the variable "self.analog_sig_source_x_1" which won't be created until later in the Python script from when this thread is started.

Hope this is useful (to you & others trying this tutorial). - MLD

On Sun, Sep 24, 2017, at 02:26 PM, Luis Felipe Albarracin Sanchez wrote:

I get o tried to do that "python  file" manually, but It did not work. Maybe I am doing it wrong. I opened opened a terminal in the folder where the python file is and I placed the manual commands that are on the tutorial, but the console shows an error. Do you know how to do this the rigth way?