Re: [python-control-discuss] NoneType and circular relative imports

[Richard M. <mu...@cd...>]

Thanks for the extra info.  I'll see if I can implement this (and install python3 so that I can test locally).  Will take until this weekend or possibly early next week (unless someone else wants to take a cut at it -:).

-richard

On 29 Oct 2012, at 13:53 , Dale Lukas Peterson <haz...@gm...> wrote:

> Richard,
>  I am running Python 3.2.  In order to run python control, I have to
> use the 2to3 tool to convert on each .py file.  It fixes things like
> print "x" by changing it to print("x").  For some reason, it is
> changing the import statements in both xferfcn.py and statesp.py from:
> 
> import statesp
> import xferfcn
> 
> to:
> 
> from . import statesp
> from . import xferfcn
> 
> Then when try to import control, I get the same error as before:
> ---------------------------------------------------------------------------
> ImportError                               Traceback (most recent call last)
> <ipython-input-1-4964879682bf> in <module>()
> ----> 1 import control
> 
> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/__init__.py
> in <module>()
>     58 # Import functions from within the control system library
>     59 #! Should probably only import the exact functions we use...
> ---> 60 from .bdalg import series, parallel, negate, feedback
>     61 from .delay import pade
>     62 from .dtime import sample_system
> 
> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/bdalg.py
> in <module>()
>     53
>     54 import scipy as sp
> ---> 55 from . import xferfcn as tf
>     56 from . import statesp as ss
>     57
> 
> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/xferfcn.py
> in <module>()
>     82 from .lti import Lti, timebaseEqual, timebase, isdtime
>     83 from warnings import warn
> ---> 84 from . import statesp
>     85
>     86 class TransferFunction(Lti):
> 
> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/statesp.py
> in <module>()
>     83 import warnings
>     84 from .lti import Lti, timebaseEqual, isdtime
> ---> 85 from . import xferfcn
>     86
>     87 class StateSpace(Lti):
> 
> ImportError: cannot import name xferfcn
> 
> I think this may stem from how src/__init__.py and each of the modules
> in src/ are importing each others functionality.  The design patterned
> that I have been following and have used with no issues in the sympy
> project can be seen in these two files:
> https://github.com/hazelnusse/sympy/blob/master/sympy/physics/mechanics/__init__.py
> https://github.com/hazelnusse/sympy/blob/master/sympy/physics/mechanics/particle.py
> 
> Basically, in each module, we set the __all__ list to include the
> names of the publicly available class and functions.  Within each
> module, we never do relative imports, we always use the absolute
> import syntax.  The __init__.py file is heavily commented so you
> should be able to see how we make those symbols available when people
> import the module or sub-package.
> 
> Luke
> 
> 
> 
> On Sat, Oct 27, 2012 at 4:54 PM, Richard Murray <mu...@cd...> wrote:
>> Both of these issues should now be fixed in the latest version of trunk.  Let me know if you continue to have problems.
>> 
>> -richard
>> 
>> On 25 Oct 2012, at 23:58 , Dale Lukas Peterson <haz...@gm...> wrote:
>> 
>>> In src/lti.py, NoneType is being imported and used in the Lti class in
>>> two locations.  Is there a reason this can't be just None?  NoneType
>>> is deprecated in Python3 and this is causing issues for me.
>>> 
>>> Also, I am getting this import error when I import control:
>>> ---------------------------------------------------------------------------
>>> ImportError                               Traceback (most recent call last)
>>> <ipython-input-1-4964879682bf> in <module>()
>>> ----> 1 import control
>>> 
>>> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/__init__.py
>>> in <module>()
>>>    58 # Import functions from within the control system library
>>>    59 #! Should probably only import the exact functions we use...
>>> ---> 60 from .bdalg import series, parallel, negate, feedback
>>>    61 from .delay import pade
>>>    62 from .dtime import sample_system
>>> 
>>> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/bdalg.py
>>> in <module>()
>>>    53
>>>    54 import scipy as sp
>>> ---> 55 from . import xferfcn as tf
>>>    56 from . import statesp as ss
>>>    57
>>> 
>>> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/xferfcn.py
>>> in <module>()
>>>    82 from .lti import Lti, timebaseEqual, timebase, isdtime
>>>    83 from warnings import warn
>>> ---> 84 from . import statesp
>>>    85
>>>    86 class TransferFunction(Lti):
>>> 
>>> /home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/statesp.py
>>> in <module>()
>>>    83 import warnings
>>>    84 from .lti import Lti, timebaseEqual, isdtime
>>> ---> 85 from . import xferfcn
>>>    86
>>>    87 class StateSpace(Lti):
>>> 
>>> ImportError: cannot import name xferfcn
>>> 
>>> I noticed that xferfcn.py has:
>>> from . import statesp
>>> 
>>> and that statesp.py has:
>>> from . import xferfcn
>>> 
>>> I am guessing is a circular dependency issue.  From what I can tell,
>>> each of these modules only imports these to do some type checking of
>>> arguments.
>>> 
>>> Luke
>>> 
>>> 
>>> --
>>> “People call me a perfectionist, but I'm not. I'm a rightist. I do
>>> something until it's right, and then I move on to the next thing.”
>>> ― James Cameron
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> 
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