Creating Python 2.7 Class

New problem with each command:

UnboundLocalError: local variable 'y' referenced before assignment

Any ideas on how to fix it?

It seems that the problem is under the def statements.

when I call on "invert_y_axis()" It gives me errors. same when I call on the zero_variables().

But when I bring out the values in zero_variables() by removing them from under that statement, and moving them to when the module is imported, I can >>> print a.

Any ideas or quick fixes?

Still no luck.  Could someone fix this code so that it works?

There is a problem with declearing variables.

You should see once you run it.

Attached is the module and the test script I am using.

Please tell me how I can fix the problem.  Nothing seems to work.

Hi - I'm still learning Python myself but I was able to get it to run by making this change to adding "a = 0" at the beginning of CMDmodule.py:

afustini@lappy486:~/Downloads$ head CMDmodule.py
# C:\python27\Lib


a = 0
'''
Invert Code for Arduino PWM when Digital
Channel is 'LOW' along with a few other
bits and pieces.
'''


##set_zero = 0

And running it seems to be ok (no error at least):

afustini@lappy486:~/Downloads$ python ./Test\ Program\ for\ CMDmodule.py
Welcome to CMDmodule.  Use Wisely. 
Valables set to Zero!
Change this value Test: 23
23
Change this value Test: 45 
45
Change this value Test:

Based on what I was reading here:

http://stackoverflow.com/questions/423379/using-global-variables-in-a-function-other-than-the-one-that-created-them

However, I'm wondering is there are reason that you are using globals heavily?  I'm still developing my sense of style for python but this would seem to be very un-"pythonic" as they say. 

I'm not sure if this will help or not, but I thought it might give an example of something I've done.  Recently I wrote a  LCD twitter display with Python.  Initially, I wrote it as a procedural program since I don't know Python that well:

https://github.com/pdp7/tweetypi/blob/master/display-hashtag.py

I'm still working on improving the code, but what I tried to do is pass data that won't change for a given instance of the HashTagDisplay class in the constructor (__init__) like the number of rows and columns for the LCD.

The constructor then sets attributes self.rows and self.cols that the methods in the HashTagDisplay class refer to.

However, I decided to pass that hashtag to search as a parameter to the HashTagDisplay.search() method which returns the results.  The HashTagDisplay.display() method then takes those results as a parameter:

My main program can thus just create a new HashTagDisplay object with the appropriate LCD parameters and then call the search and display methods in a loop:

I think that you should be able avoid globals by either setting attributes in an object or passing parameters to a method and utilizing the return value.

Drew Fustini wrote:

 

Hi - I'm still learning Python myself but I was able to get it to run by making this change to adding "a = 0" at the beginning of CMDmodule.py:

 

afustini@lappy486:~/Downloads$ head CMDmodule.py
# C:\python27\Lib


a = 0
'''
Invert Code for Arduino PWM when Digital
Channel is 'LOW' along with a few other
bits and pieces.
'''


##set_zero = 0

 

And running it seems to be ok (no error at least):

 

afustini@lappy486:~/Downloads$ python ./Test\ Program\ for\ CMDmodule.py
Welcome to CMDmodule.  Use Wisely. 
Valables set to Zero!
Change this value Test: 23
23
Change this value Test: 45 
45
Change this value Test: 

 

Based on what I was reading here:

 

http://stackoverflow.com/questions/423379/using-global-variables-in-a-function-other-than-the-one-that-created-them

 

However, I'm wondering is there are reason that you are using globals heavily?  I'm still developing my sense of style for python but this would seem to be very un-"pythonic" as they say. 

You have seen first hand the problem I am having!

Change this value Test: 23

23

It should have applied the formula in CMD module:

def pwm_formula_test(self):

        global a

        PWM = 255

        aa = PWM*a

        aa = round(aa, 1)

        motor_a = aa

Well... I think yours might be a bit different but you get the idea.

It should have mulitpled '23' by 255 and then given the output.

Any ideas why it is not working?

Drew Fustini wrote:

 

Hi - I'm still learning Python myself but I was able to get it to run by making this change to adding "a = 0" at the beginning of CMDmodule.py:

 

afustini@lappy486:~/Downloads$ head CMDmodule.py
# C:\python27\Lib


a = 0
'''
Invert Code for Arduino PWM when Digital
Channel is 'LOW' along with a few other
bits and pieces.
'''


##set_zero = 0

 

And running it seems to be ok (no error at least):

 

afustini@lappy486:~/Downloads$ python ./Test\ Program\ for\ CMDmodule.py
Welcome to CMDmodule.  Use Wisely. 
Valables set to Zero!
Change this value Test: 23
23
Change this value Test: 45 
45
Change this value Test: 

 

Based on what I was reading here:

 

http://stackoverflow.com/questions/423379/using-global-variables-in-a-function-other-than-the-one-that-created-them

 

However, I'm wondering is there are reason that you are using globals heavily?  I'm still developing my sense of style for python but this would seem to be very un-"pythonic" as they say. 

You have seen first hand the problem I am having!

Change this value Test: 23

23

It should have applied the formula in CMD module:

def pwm_formula_test(self):

        global a

        PWM = 255

        aa = PWM*a

        aa = round(aa, 1)

        motor_a = aa

Well... I think yours might be a bit different but you get the idea.

It should have mulitpled '23' by 255 and then given the output.

Any ideas why it is not working?

I think it must be due to some aspect of using globals.  I would think globals wouldn't be the best way to handle this anyways.  What do you think of changing pwm_formula_test() to accept a parameter and then having it return a value?

afustini@lappy486:~/Downloads$ python ./Test\ Program\ for\ CMDmodule.py

Welcome to CMDmodule.  Use Wisely.

Valables set to Zero!

Change this value Test: 25

6375.0

so that method in your class would be:

    def pwm_formula_test(self, a):

        PWM = 255

        aa = PWM*a

        aa = round(aa, 1)

        motor_a = aa

        return aa

and you test script would have:

while True:

    a = input("Change this value Test: ")

    b = CMD.pwm_formula_test(a)

    print b

I don't mind how it goes about solving the problem.  I just want it to work.

I was using globals because I read somewhere that 'that was the go'.  I don't know any better.

Does the way you suggested above work?

The snippets I posted above in http://www.element14.com/community/message/65629#65661 do work.

This adds a parameter "a":

    def pwm_formula_test(self, a):

"a" is then multiplied by 255 ("PWM" value) and stored in "aa".  "aa" is the rounded to one decimal place.  The method returns the value of "aa".  This is value stored in "b":

    b = CMD.pwm_formula_test(a)

I'm a little unclear as to the objective of your program though.  What is the objective?

That is correct.  Thank you.  I will test it later.

But what if I want to use the fomula for a different variable?

I'm a little unclear as to the objective of your program though.  What is the objective?

The objective is to read imput from  a joystick and then make the values go through that formula so that they can be read correctly by the arduino.

This branch of the project is so that it is easier for others to understand the code.  I want to eventually write a 'guide' so that others can replicate this project.  Having little pieces of code in a library/class should make it easier for others to learn.

I posted here:  http://www.raspberrypi.org/phpBB3/viewtopic.php?p=225261#p225261  all the different things I am using to make this work.  That is just another little issue I am having with the Gertboard but for the same project.

Hope that helps clear up your understanding.

But what if I want to use the fomula for a different variable?

Do you mean pass a different variable to the pwm_formula_test() method?  You can just call it again with a different value as the parameter.  Is that what you mean?

yep. I will look at this some other time.  Other parts of the project must be completed first.  This was just to kill some time and build apon my own knowledge of python.

Thanks for all your help.