File "<string>", line 19, in <module> error is related to what?

[menator01]

My guess is you have a hidden character.
I tried your code from copy and paste and got the same error but, when I typed it in it worked as expected.

class Portfolio:
    def __init__(self):
        self.holdings = {}

    def buy(self, ticker, shares):
        self.holdings[ticker] = self.holdings.get(ticker, 0) + shares

    def sell(self, ticker, shares):
        self.holdings[ticker] = self.holdings.get(ticker, 0) - shares

    def __iter__(self):
        return iter(self.holdings.items())


p = Portfolio()
p.buy('Alpha', 15)
p.buy('Beta', 23)
p.buy('Gamma', 9)
p.buy('Gamma', 20)
p.sell('Beta', 5)

str_len = len(max(p)[0])

for (ticker, shares) in p:
    if len(ticker) < str_len:
        spacer = ' '*(str_len - len(ticker) + 2)
    else:
        spacer = ' '*2
    print(f'{ticker} {spacer} {shares}')

Output:
Alpha    15
Beta     18
Gamma    29