Why am I getting list elements < 0 ?

[Mark17]

Hi all!

Here's some code:

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price_chg = np.arange(-10,11,2)   stock_prices = [100]   for i in range(10001):     if (stock_prices[-1] + np.random.choice(price_chg)) < 0:         stock_prices.append(0)         continue     else:         stock_prices.append(stock_prices[-1] + np.random.choice(price_chg))

Why is the if block failing to keep negative integers out of the list?

[ibreeden]

Why is the if block failing to keep negative integers out of the list?

Because you are generating a new random price in the "else" block which can again be negative.
Apparently you mean to do this:

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price_chg = np.arange(-10,11,2)    stock_prices = [100]    for i in range(10001):     random_price = stock_prices.append(stock_prices[-1] + np.random.choice(price_chg))     if random_price < 0:         stock_prices.append(0)     else:         stock_prices.append(random_price)

[Mark17]

Why is the if block failing to keep negative integers out of the list?

Because you are generating a new random price in the "else" block which can again be negative.
Apparently you mean to do this:

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price_chg = np.arange(-10,11,2)    stock_prices = [100]    for i in range(10001):     random_price = stock_prices.append(stock_prices[-1] + np.random.choice(price_chg))     if random_price < 0:         stock_prices.append(0)     else:         stock_prices.append(random_price)

When will the "stupid mistakes" end? Rhetorical question. :)

Thank you!

[deanhystad]

max() may be a better choice.

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import random price = 10 stock_prices = [price] for _ in range(11):     price = max(0, price + random.randrange(-10, 11, 2))     stock_prices.append(price)   print(stock_prices)

[naughtyCat]

One line code

1 2	import random stock_prices = [10] + [max(0, 10+random.randrange(-10, 11, 2)) for _ in range(11)]

[deanhystad]

Not the same result. +/-10 is the range of daily fluctuation, not the range of stock_prices.

[naughtyCat]

Not the same result. +/-10 is the range of daily fluctuation, not the range of stock_prices.

two line

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import random price = 10 stock_prices = [price] + [max(0, price+random.randrange(-10, 11, 2)) for _ in range(11)]

[deanhystad]

Still not right. The price fluctuates from the previous day, not the first day. I don't think this can be done with a comprehension because there is no mechanism for remembering what the price was yesterday.

[naughtyCat]

Still not right. The price fluctuates from the previous day, not the first day. I don't think this can be done with a comprehension because there is no mechanism for remembering what the price was yesterday.

ya, you are right, I am learned, thanks