I am trying to write a function to calculate RSI data using input from a list or by pulling live price data from an API.

The script worked fine when feeding it data directly from a list, but while I am trying to convert it to a function, I am experiencing issues.

The function needs to remember the output from a previous run in order to calculate a smoothed average, but I keep getting an error that the local variable is being called before assignment. I've eliminated a lot of the code to keep the post short, but it errors on the 15th run. On the 14th run I think I am defining the variable and printing the value, so I don't understand why it errors.

def calc_rsi(price, i):
     while price != complete:
        window.append(price)

        if i == 14:
            avg_gain = sum(gains) / len(gains)
            avg_loss = sum(losses) / len(losses)
           

        if i > 14:
            avg_gain = (prev_avg_gain * (window_length - 1)   gain) / window_length
            avg_loss = (prev_avg_loss * (window_length - 1)   loss) / window_length


        if i >= 14:
            rs = avg_gain / avg_loss
            rsi = round(100 - (100 / (1   rs)), 2)
            prev_avg_gain = avg_gain
            prev_avg_loss = avg_loss
            print ("rsi", rsi)
            print ("gain", prev_avg_gain)
            print ()

The thing that is throwing me for a real loop (pun intended) is that on run 14, my print statement 'print ("gain=", prev_avg_gain)' returns the proper value, so I know that it is assigning a value to the variable.... I've tried adding the 'prev_avg_gain = avg_gain ' to the block of code for 'if i == 14:' and 'if i > 14:' rather than doing it once in the >= block and it throws the same error.

I am new to python and scripting so please go easy :)

CodePudding user response：

I got some help on a different forum and I still don't understand exactly why, but I guess python resets the 'prev_avg_gain' variable every time it looped so to fix this I created a dictionary outside of the function and updated the dictionary with the variable data when required.

prev_avg = {}
# Calculate Price Differences
def calc_rsi(price, i):
    
    while price != "complete":
        window.append(price)
        # print (i)
        
        
    # Calculate Average Gains and Losses
            if i == 14:
                avg_gain = sum(gains) / len(gains)
                avg_loss = sum(losses) / len(losses)
               

            if i > 14:
                avg_gain = (prev_avg["prev_avg_gain"] * (window_length - 1)   gain) / window_length
                avg_loss = (prev_avg["prev_avg_loss"] * (window_length - 1)   loss) / window_length
                # prev_avg_gain = avg_gain
                # prev_avg_loss = avg_loss
                # print (output)

            if i >= 14:
                rs = avg_gain / avg_loss
                rsi = round(100 - (100 / (1   rs)), 2)
                
                prev_avg["prev_avg_gain"] = avg_gain
                prev_avg["prev_avg_loss"] = avg_loss
                # print ("rsi", rsi)
                # print ("gain", prev_avg["prev_avg_gain"])
                # print ()

CodePudding user response：

The code as you have pasted will work, if you make one call to calc_rsi() where i is incremented from <=14 to >14. In this case prev_avg_gain will be remembered. But if you make 2 calls to calc_rsi() then prev_avg_gain will not be remembered between calls.

To demonstrate, I use a trimmed down example:

def calc_rsi(price, i):
     while i <= price:
        if i == 14:
            avg_gain = 10

        if i > 14:
            avg_gain = (prev_avg_gain * (10 - 1)   1) / 5

        if i >= 14:
            prev_avg_gain = avg_gain
            print ("gain", prev_avg_gain)

        i  = 1

# i loops from 13 to 16 in one call, this works!
calc_rsi(price=16, i=14)

# i loops from 13 to 14, prev_avg_gain is set
calc_rsi(price=14, i=13)
# i loops from 15 to 16, throws error! because prev_avg_gain is not remembered
calc_rsi(price=16, i=15)