How to access variables from other functions in python

Question

I've got a function (get_score) that uses variables from other functions(self.__sma) in the same class.

My question: How can I access these variables from the get_score function? (error: global name is not defined).

Also, i heard that using global variables causes a shitstorm(just based from what I read on here). Thanks in advance.

Here is some code:

testlist = ['TREE', 'HAPPY']
Class MyStrategy(strategy.BacktestingStrategy):
    def __init__(self, feed, instrument):
        super(MyStrategy, self).__init__(feed, 1000)
        self.__position = [] #None
        self.__instrument = instrument
        self.setUseAdjustedValues(True)
        self.__prices = feed[instrument].getPriceDataSeries()
        self.__sma = ma.SMA(feed[instrument].getPriceDataSeries(), smaPeriod)

    def get_score(self,banana)
        fruit_lover= self.__sma
        return fruit_lover + banana

    def onBars(self, bars):
        for x in bars.getInstruments():

            list_large = {}
            for y in testlist: 
                list_large.update({y : self.get_score(5)})

I've seen quite a few questions like this, search before asking — Eric
– Eric, Commented Nov 26, 2016 at 3:12
I did, I am, actually having a hard time with this...a link would be great...found a few pages but its still not working. — RageAgainstheMachine
– RageAgainstheMachine, Commented Nov 26, 2016 at 3:19
A function called get_score should get / return a score, not set some variables. Along with that point, {y : self.get_score(5)} is setting y to None — OneCricketeer
– OneCricketeer, Commented Nov 26, 2016 at 3:19
sorry, I didint accurately write the code, just edited it. The get_score function does actually return something and "y" is a variable in the testlist list(at the top of the page). — RageAgainstheMachine
– RageAgainstheMachine, Commented Nov 26, 2016 at 3:24
Is it possible its the 2 underscores in "self.__sma" that are making it private and therefore inaccessible?? — RageAgainstheMachine
– RageAgainstheMachine, Commented Nov 26, 2016 at 3:51

hpaulj · Accepted Answer · 2016-11-26 08:19:14Z

With a copy of your script, and a bunch of stubs, and too many syntax corrections:

testlist = ['TREE', 'HAPPY']
class MyStrategy(): #strategy.BacktestingStrategy):  # lowercase class
    def __init__(self, feed, instrument):
        #super(MyStrategy, self).__init__(feed, 1000)
        self.__position = [] #None
        self.__instrument = instrument
        #self.setUseAdjustedValues(True)
        self.__prices = 123 #feed[instrument].getPriceDataSeries()
        self.__sma = 100 # ma.SMA(feed[instrument].getPriceDataSeries(), smaPeriod)

    def get_score(self,banana):   # add :
        fruit_lover= self.__sma
        return fruit_lover + banana

    def onBars(self, bars):
        #for x in bars.getInstruments():
        list_large = {}
        for y in testlist: 
            list_large.update({y : self.get_score(5)})  
        self.list_large = list_large  # save list_large 
s = MyStrategy('feed', 'inst')
print(vars(s))           # look at attributes set in __init__
print(s.get_score(10))   # test get_score by itself
s.onBars('bars')         # test onBars
print(s.list_large)

I get the following run:

0009:~/mypy$ python stack40814540.py 
{'_MyStrategy__position': [], 
 '_MyStrategy__instrument': 'inst', 
 '_MyStrategy__sma': 100, 
 '_MyStrategy__prices': 123}
110
{'TREE': 105, 'HAPPY': 105}

I have no problem accessing __sma attribute in the other methods.

Because the name starts with __ (and not ending __), it is coded as a 'pseudo-private' variable, as can be seen in the vars display. But that doesn't harm access from another method.

For a beginner I'd suggest skipping that feature, and just use names like self.sma. Code will be easier to debug.

Make sure you understand my changes; and run some similar tests.

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