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Re: [python-control-discuss] NoneType and circular relative imports
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From: Dale L. P. <haz...@gm...> - 2012-10-29 20:53:30
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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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--
“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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