## What will we cover in this tutorial?

In this tutorial we will cover the following

- Read historic time series data from
**Yahoo! Finance**using**Pandas-Datareader**. - Calculate the
**Average True Range (ATR)**. - Visualize it on a chart.

## Step 1: Read historic stock prices from Yahoo! Finance API

To read data from Yahoo! Finance API we use Pandas-Datareader, which has a direct method.

This requires that we give a start date on how old data we want to retrieve.

```
import pandas_datareader as pdr
import datetime as dt
start = dt.datetime(2020, 1, 1)
data = pdr.get_data_yahoo("NFLX", start)
print(data.tail())
```

This we result in similar output.

```
High Low Open Close Volume Adj Close
Date
2021-02-12 561.250000 550.849976 556.940002 556.520020 2195900 556.520020
2021-02-16 563.630005 552.729980 557.289978 557.280029 2622400 557.280029
2021-02-17 555.250000 543.030029 550.989990 551.340027 2069600 551.340027
2021-02-18 550.000000 538.229980 549.000000 548.219971 2456200 548.219971
2021-02-19 548.989990 538.809998 548.000000 540.219971 2838600 540.219971
```

## Calculate the Average True Range (ATR)

The Average True Range (ATR) is calculated as follows, as **investopedia.org** defines it.

This can be calculated as follows.

```
import numpy as np
import pandas_datareader as pdr
import datetime as dt
start = dt.datetime(2020, 1, 1)
data = pdr.get_data_yahoo("NFLX", start)
high_low = data['High'] - data['Low']
high_close = np.abs(data['High'] - data['Close'].shift())
low_close = np.abs(data['Low'] - data['Close'].shift())
ranges = pd.concat([high_low, high_close, low_close], axis=1)
true_range = np.max(ranges, axis=1)
atr = true_range.rolling(14).sum()/14
```

Where we use the 14 days standard.

## Visualize the ATR and the stock price

We will use **Matplotlib** to visualize it as it integrates well with DataFrames from Pandas.

```
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
atr.plot(ax=ax)
data['Close'].plot(ax=ax, secondary_y=True, alpha=0.3)
plt.show()
```

This will result in a chart similar to this one.

## Want to learn more?

Check out this full FREE course learning about Risk and Return with Pandas DataFrames (Python).

Hello Rune…why are you still dividing the value for the ATR by 14 when you already have the rolling mean of 14

Hi Ricky,

Yes, it could have been done by using rolling mean.

Notice I did it with sum instead. Just to follow the formula from Investopedia.org.

`true_range.rolling(14).sum()/14`

Cheers,

Rune

Not bad, but you’re missing one line of code: import pandas as pd

Hi Geoff,

Great point.

It can be imported – but as we do not use any direct methods from pandas, it is enough to use it from the pandas_datareader.

Cheers, Rune

I need a set of codes from the Panda Library

Necessary in the fastest time with its data.

Thank you

Hi Bahaa,

Great to connect with you.

Not sure what you are lookin for?

This example used Pandas-datareader to get the data returned in a DataFrame (Pandas) to make the calculation.

Cheers,

Rune

Why does the ATR calculation results in different values than the ATR calculation in Tradingview or other Platforms on the the same instrument with the same lookback period?

Hi Mark,

Great question.

I have just checked the calculations – they are corresponding to the ones on Investopedia.org. Maybe they are not the same they use on platforms you compare with.

Cheers, Rune

The final ATR is incorrect. When you are pulling the max in the true_range dataframe, that is when the issue occurs. Because you have used the shift() in the other series, the max, just takes the high_low series and it is assigned as max for that row – this causes the whole rolling.sum()/14 part to pull incorrect values, resulting in an incorrect final ATR.

Let’s see if we can figure it out.

We have:

TR = max( (H – L), | H – C_p | , | L – C_p | )

n: 14

H (current high): data[‘High’]

L (current low): data[‘Low’]

C_p (Previous close): data[‘Close’].shift()

Notice that the shift ( data[‘Close’].shift() ) is used to get the previous close. And yes, that means the first value will be NaN.

That should make:

TR = max( data[‘High’] – data[‘Low’], abs( data[‘High’] – data[‘Close’].shift() ), abs( data[‘Low’] – data[‘Close’].shift() ) )

That can be converted to:

high_low = data[‘High’] – data[‘Low’]

high_close = abs(data[‘High’] – data[‘Close’].shift())

low_close = abs(data[‘Low’] – data[‘Close’].shift())

ranges = concat([high_low, high_close, low_close], axis=1)

TR = max(ranges, axis=1)

I am not sure where the mistake should be?

Don’t get me wrong – I am curious too?

P.S.: I have tried using truncate but with no success

If you have a solution to this, I would really appreciate it. Thank you.

Thank you Rune!

Getting up to speed w/ Python myself and was actually coding a strategy for trading when I found your code. Cool stuff that saved me time and I learned few tricks in manipulating dataframes.

I find your results inline with mine from an excel spreadsheet and TOS. Only exception could be the 1st TrueRange whose calculation is limited to “High-Low”, lacking the previous Close value from the dataset.

If compared to Tradestation or any platform with full dataset, starting before datetime(2020, 1, 1), you’ll get a different result on this one.

Same on the 1st ATR which does include this 1st TR ðŸ™‚

Hi Jean-Marc,

Thanks for the feedback.

The 1st row of data is incomplete, as it does not have previous close. Also the first 14 values of ATR are not correct, as the data to calculate them are not present. To deal with that you can read more data and discard them, as you also say.

If you have more insights in other differences with the calculations of ATR and tranding platforms, please let me know.

Cheers, Rune

There are multiple different common ways to calculate ATR. They may be a simple moving average, a weighted moving average, or even a Wilder’s calculation. For a quick examination, you can look at this source https://www.macroption.com/atr-excel/

Thank you for sharing. I will be looking into it. Cheers.

Yep, that’s why people are getting differing results from trading platforms. Also, several platforms may not use the ‘standard’ 14-day window. It may be a 21-day, 50-day, etc. The use of exponential weighted moving average versus simple moving average versus weighted with alpha correction will also result in somewhat different numbers. In the end, I’m not sure that all matters much except that it’s worth being aware when the numbers don’t align with another source. In the end, it’s only ‘context’ for trading and nothing hard and fast, anyway. ATR is a great tool to get some idea of position sizing for expected losses (stop losses) as it’s a volatility metric.

Also, my apologies for the earlier mistake regarding the Pandas DataReader. I was up tinkering around at 1 AM on some night I should have been in bed and used my own code with my own data source (Tiingo.com) and then used a direct CSV import. In my exhaustion I had forgotten that I had altered portions of your code and then corrected you for my own error in translation.

Hi Geoff,

Thank you for sharing such a detailed answer.

Cheers,

Rune

Hi Rune, and thank so much for your fantastic work. I have a question, all it’s ok for simple stock but when I want to use the same strategy for a multiindex dataframe the final dataframe its only one column. Please I apreciate if you could help me to solve that.

Hi Hugo, just be sure how the DataFrame is structured. This would be the case when you get a DataFrame from something like this:

data = pdr.get_data_yahoo([“NFLX”, “AAPL”, “TWTR”], start)

?

We should have a column for each stock but the output only give one:

[*********************100%***********************] 3 of 3 completed

Date

2020-01-02 NaN

2020-01-03 NaN

2020-01-06 NaN

2020-01-07 NaN

2020-01-08 NaN

…

2022-01-05 13.772858

2022-01-06 14.377860

2022-01-07 14.642147

2022-01-10 14.552861

2022-01-11 14.535714

Length: 512, dtype: float64

This should do the trick:

`import numpy as np`

import pandas_datareader as pdr

import pandas as pd

import datetime as dt

`start = dt.datetime(2020, 1, 1)`

tickers = ["NFLX", "AAPL"]

data = pdr.get_data_yahoo(tickers, start)

`high_low = data['High'] - data['Low']`

high_close = np.abs(data['High'] - data['Close'].shift())

low_close = np.abs(data['Low'] - data['Close'].shift())

`ranges = pd.concat([high_low, high_close, low_close], axis=1)`

`true_range = pd.DataFrame()`

for ticker in tickers:

true_range[ticker] = np.max(ranges[ticker], axis=1)

`atr = true_range.rolling(14).sum() / 14`

`print(atr)`

Perfect!, Thank you.