How to force usage of python 3 in cocotb?

Question

I'm using CocoTB to test my HDL design, but as I understand, it's possible to use it with python2.7 or python3.

In setup.py config file I can see that both are supported :

    [...]
    "Programming Language :: Python :: 2.7",
    "Programming Language :: Python :: 3",
    [...]

In endian_swapper test (examples/endian_swapper/tests/test_endian_swapper.py), if I modify a test script to see which version is used :

@cocotb.test()
def wavedrom_test(dut):
    """
    Generate a JSON wavedrom diagram of a trace and save it to wavedrom.json
    """
    print("Python version used {}".format(sys.version_info))

I can see that python2.7 is used when I launch test with «make» command :

Python version used sys.version_info(major=2, minor=7, micro=9, releaselevel='final', serial=0)

My python3 executable is named ... python3 in fact (debian). Is there a canonical way to force cocotb to use python3 instead of python2 ?

My workaround is to use a virtualenv. Make sure you activate the virtualenv before compiling the first time or use make clean to rebuild the .so files against the right version of python. — Evan, May 02 '19 at 17:30

score 1 · Answer 1 · answered Oct 08 '19 at 13:27

I found a proper way to do it.

First download the last version of python on the official website :

$ wget https://www.python.org/ftp/python/3.7.4/Python-3.7.4.tar.xz

Then unflat it and configure it with the option --enable-shared

$ tar -Jxvf Python-3.7.4.tar.xz
$ cd Python-3.7.4
$ ./configure --enable-shared
$ make
$ sudo make install

Once installed go to your cocotb test directory then install virtual environment :

$ export LD_LIBRARY_PATH=/usr/local/lib
$ virtualenv --python=/usr/local/bin/python3.7 envp37
$ source envp37/bin/activate
$ python -m pip install cocotb

Then you can launch your cocotb test environment with traditional make :

$ make

Dectivate the python environment with :

$ deactivate

score 1 · Accepted Answer · answered Jun 04 '20 at 11:32

try updating the PATH variable. worked for me.
when cocotb looks for python, it looks for it at the folders that are listed at the PATH variable.
let say that your python3 full path is at
/usr/bin/python3
(you can find python3 full path by which python3)
i also added here link to new place in case both python2 and python3 are at the same folder...

> python -V
Python 2.7.17
> ln -s /usr/bin/python3 /home/$USER/python
> export PATH="/home/$USER:$PATH"
> python -V
Python 3.6.9

Thanks lisrael1, your solution is better than mine. You don't have to compile other python3 than the one in your distribution. — FabienM, Jun 04 '20 at 11:41

score 0 · Answer 3 · answered Apr 01 '19 at 08:08

I found solutions on linuxconfig.org, thanks to themperek. But it's not exactly what I want.

The alias solution doesn't work for me. The update-alternative works but only with «official» python3 installed on debian. I can't use an alternative (3.7) manually installed.

$ sudo update-alternatives --config python
There are 3 choices for the alternative python (providing /usr/bin/python).

  Selection    Path                Priority   Status
------------------------------------------------------------
  0            /usr/bin/python3.7   2         auto mode
  1            /usr/bin/python2.7   0         manual mode
  2            /usr/bin/python3.4   1         manual mode
* 3            /usr/bin/python3.7   2         manual mode

Press enter to keep the current choice[*], or type selection number: 3
$ make clean;make
0.00ns INFO     Running on Icarus Verilog version 11.0 (devel)
0.00ns INFO     Python interpreter initialised and cocotb loaded!
0.00ns INFO     Running tests with Cocotb v1.0.1 from /opt/cocotb
0.00ns INFO     Seeding Python random module with 1554105931
0.00ns INFO     Found test test_ttl.ttl_test
0.00ns INFO     Running test 1/1: ttl_test
0.00ns INFO     Starting test: "ttl_test"
                Description:  simple ttl test function 
[...]
3.4.2 (default, Feb  7 2019, 06:11:23) 
[...]

How to force usage of python 3 in cocotb?

3 Answers3