Webscraping with Python

This is some code I wrote to scrape stock prices with Python. I wrote it on Jupyter notebook.

First off you’ll need chromedriver (Google “download chromedriver” and get the file on the first link. Put it in the folder with your Jupyter notebook.

Next, you’ll need a bunch of libraries, some of which will need to be pip installed.

from selenium import webdriver
import datetime
import time
from multiprocessing import Pool,TimeoutError
import urllib.request
import re
from urllib.error import URLError, HTTPError

In the code below, you won’t need all of this, but I’m just copying the entire import section of my code.

Next, we’ll fire up a browser.

driverspy = webdriver.Chrome()
driverspy.get(‘https://finance.yahoo.com/quote/SPY?p=SPY’)

This should open a python controlled browser that surfs its way to Yahoo Finance and loads up the page for SPY (a popular S&P 500 ETF).

Finally, we’ll define a function to scrape the price and then scrape the price off this page.

sourcespy = driverspy.page_source
found = re.search(‘”35″>(\d+\.\d+)</span>’, sourcespy).group(1)

If you look at the html code of the page_source of the Yahoo page with the SPY data, you’ll see it has, buried in it, something that looks like this:

<span class=”Trsdu(0.3s) Fw(b) Fz(36px) Mb(-4px) D(ib)” data-reactid=“35”>283.82</span><span class=”Trsdu(0.3s) Fw(500) Pstart(10px) Fz(24px) C($dataGreen)” data-reactid=”36″>+1.72 (+0.61%)</span><div

We rely on the bolded part always being the same (“35″> … </span> and encapsulating the bold+underlined price (283.82) to extract the price. The \d+.\d+ tells Python to look for a positive number, a period and another positive number.

Now, we have a basic scraper to get prices from Yahoo finance. If we set up a loop, we can get prices every few minutes and generate a time series dataset.

Python Basics

I recently learned and started using Python for some of my projects. Python is a high level programming language with a number of pre-programmed packages for a variety of useful tasks. Tasks I’ve used Python for include scraping the web for data (excellent!), machine learning (meh … but that’s more my fault than Python’s), OCR (super meh), and algorithmic name classification, such as gender determination (again, excellent!).

While I will not provide direct code to perform predictive analysis using Python, I will use this post to link to a variety of resources that I have used, along with how I use it.

First, how to get started with Python. I use Jupyter Notebook, along with Anaconda. Both of these are installed when you download and install the latest version of Anaconda – google “download jupyter notebook” and go to the first link. The actual download will be from the Anaconda website.  As of posting, the latest version is Python 3.6. Click “Download,” run the file and choose all the default options and install Python and Jupyter Notebook.

Jupyter Notebook runs inside your browser. Open up Jupyter Notebook, create a folder for coding, and then create a new Notebook. Each Notebook has distinct cells for distinct blocks of code that can be run separately. Once you run the code in a cell, the output is produced right below. Here is an example:

Capture2

 

As you can see, when you run each cell, it simply generates the output right below. One thing I wanted to point out is that variables and variable types are generated dynamically. the code “a=1″ first defined a as an integer and then sets it to two. Printing (and other functions) can be applied to integers (e.g. “print(a)”) or strings (e.g. print(‘hello world’)) but not to a mix (see the error in the second cell).

The second thing (and I love this) is the indentation is part of the language.

if 3>2:

print(‘hi’)
print(‘there’)

will return

hi
there

if 3<2:

print(‘hi’)
print(‘there’)

will return nothing

but

if 3<2:

print(‘hi’)

print(‘there’)

will return

there

The indentation controls what is run in the “if” statement. This forces discipline in generating readable (and workable) code.

Once you’ve gotten Python up and running – you’ll need additional packages to do other code.

For webscraping, I’d recommend selenium and chromedriver.

For OCR, I’d recommend Tesseract (Google’s OCR).

For machine learning, I use (but don’t know enough to recommend) tensorflow.

 

 

Limited attention and …

One part of my academic research agenda deals with the effects of limited attention on professional investing. This paper uses marital events as a shock to attention and shows how managers behave differently when they’re getting married or divorced. We find that managers in general become less active in their trading/investing, suffer from behavioral biases more, and perform poorer.

This past semester, I moved from the Univ. of Florida to the Univ. of Alabama and prepped a couple of new classes. While not as stressful as marriage or divorce, I did devote a bit less time to my portfolio this semester … so what happened in my case?

The biggest change was (1) I rebalanced less… I probably ran my screen once or twice the entire semester to look for equities to deploy assets to. (2) I did not, even once, look for improvements to my screens or run any of my secondary screens.

The effects were not immediately felt on performance, but I suspect if I continued on this “autopilot” path, so to speak, the end result would be a less than manicured portfolio and eventually, a stale and less than robust investment screen. All in all, I feel my personal experience is consistent with what we found in the paper above.

Change … in general

With my recent move to the University of Alabama from the University of Florida, I starting thinking about the topic of change. In the context of quantitative investing, I started thinking about changes in basic rules that we take for given when investing quantitatively and what we can do about them.

Here’s an example – academics have long taught the CAPM, a model that predicts that companies with higher systematic risk (risk stemming from overall market conditions) should outperform companies with lower systematic risk. This makes intuitive sense… riskier companies, especially companies with higher risk exposure to overall economic conditions *should* give higher returns, on average. The empirical evidence in the 70s and 80s (in hindsight) was mixed, but in general we accepted this wisdom.

However, starting in the 1990s, we started to question this basic assumption. Fama French 1992, Table II documented this:

betaret

Companies are sorted by “pre-ranking betas” (simply the beta estimated using data from before the period we measure the returns) and the average monthly returns for the next year, by pre-beta deciles are presented. 1A and 1B are the 0-5% and 5-10% comapnies by pre-rnaking beta, 2-9 are the 2nd through 9th decile by pre-ranking beta, 10A and 10B are the 90-95% and 95-100% of firms by preranking beta.

Fama and French wrote, “the beta-sorted portfolios do not support the [CAPM]. … There is no obvious relation between beta and average returns.” [disclaimer: to my eyes, if I squint hard enough, I can sort of see a slight increase in average returns with beta, but the magnitude and monotonicity of the effect are both questionable.]

And so the decline of empirical belief in the CAPM started, and today, there is little faith that stocks with high market betas will outperform the market (although the CAPM is still widely taught). (see, for example “Is Beta Dead” from the Appendix of a popular Finance Textbook. )

In fact, the academic literature has made something of a 180 on this topic. The new hot anomaly is “low vol,” or “low beta.” This literature around this anomaly shows that the low volatility/low beta stocks actually outperform high volatility/high beta stocks and proposes several stories as to why this might be the case. If something so firmly grounded in theory can experience so complete a change, I think it’s a cautionary tale for *all* quantitative strategies … all things (including both the CAPM Beta and my time at Florida), run their course eventually.

 

 

 

Momentum Across Anomalies

In a new academic piece, we examine whether anomalies themselves exhibit momentum. Momentum in the context of investing refers to the idea that stocks that have done well recently continue to do well and stocks that have done poorly recently continue to do poorly. The momentum anomaly in stocks was widely publicized by Jagadeesh and Titman in their 1993 paper titled, “Returns to Buying Winners and Selling Losers: Implications for Stock Market Efficiency.”

We find this same idea holds for anomalies themselves. Examining 13 anomalies, we find anomalies that have performed well recently (in the last month), continue to do well next month. Anomalies that have been performing poorly recently continue to experience poor performance going forward. A chart makes this clear:

anomom

The chart documents the evolution of $10,000 invested in one of three strategies. The top line is a strategy that invests each month in the top half of the 13 anomalies (7 since investing in 6½ anomalies is hard) being analyzed, based on the 13 anomalies’ performance in the previous month. So, for example, if the value, momentum, size, profitability, accruals, investment level, and O-score anomalies did better than the other 6 anomalies we analyzed\ last month, the strategy would equally invest in these 7 anomalies. The bottom line does the opposite, investing in the bottom 6 anomalies and the middle line equally invests in all 13 anomalies across the entire period.

From the chart, it is clear that anomalies themselves exhibit momentum and the result is robust to the usual battery of academic tests. From a practitioner’s perspective, the implication is clear: if you’re interested in smart beta type investing, pick a strategy (or strategies) that has been doing well recently. From an academic’s perspective, the more interesting question is why. If you’re interested in our take on reasons for this, you can read our paper for some reasons we think we observe this momentum across anomalies.

 

Why invest quantitatively?

My current academic research currently focuses on personal characteristics of investors (specifically hedge fund managers) and how these characteristics affect their investments. For example, my paper on hedge fund managers’ marriages and divorecs shows that fund performance suffers during both marriages and divorces and argues this is a results of manager distraction from personal events. Another paper on hedge fund managers’ cars shows that fund managers who drive performance cars take more risks, without yielding additional returns.

This general agenda has led me to the firm belief that investors are swayed by behavioral biases in their investments. These biases can be the result of some intrinsic characteristic (such as a desire for sensation seeking, which leads to a preference for fast cars and risk in investments) or some time varying affect (such as a distraction from a major life event). Either way, these biases are hazardous to investment performance.

Quantitative investing gives an easy out to these biases. If we follow a fixed set of rules  when investing (and are faithful in following them), there’s no room for behavioral biases to creep in. A computer, relying on objective data from the markets, tells us what to buy and sell when. Getting married? No problem – just let the computer tell you what to do. Getting divorced? Same deal. Inherently a risk taker? There’s no scope for your gambling ways to affect your investing. Risk averse to the extreme? Again… no way for your timidity to stymie your investing.

This is one of the big advantages of quantitative investing.

Long short strategies at a time when we are at all time highs

Markets are at all time highs – this is not uncommon – markets (since they are supposed to go up) should be at, or near, all time highs much of the time. That doesn’t mean that investors cannot be nervous about this condition. A number of respected investors will encourage caution, citing “all-time highs” as a reason for caution. The worry, of course, is that the market will come crashing down.

spy

(SPY at all time highs right now!)

Long short strategies, which have both long, and short positions are a nice way to hedge against the potential of a large market downturn. When engaging in a long short strategy, the first decision to make is are you going to be completely hedged (that is, your long positions and short positions are roughly equal, in terms of market sensitivity), or are you going to have a long or short bias. This is ultimately a decision that resolves into the question, “can you time the market?” There are many perspectives on this, but my take is that this is hard to do and I am not going to focus on this.

Rather, I will focus on a question that arises once you have decided on a net exposure: what should you be long? and what should you be short? Some solutions include:

1. Going long and short completely separate strategies – for example, profitability for a long strategy and some short screen for a short. This has the advantage in that you are, at least in back tests, gaining on both ends. However, we know nothing about the correlations of the long and short legs and there may be situations in which we lose money on both ends if the long leg goes down and the short leg goes up!

2. Going long and short separate ends of a single spectrum. For example, if we are separating stocks in the universe based on the PE measures, perhaps we go long low PE stocks (value stocks) and short high PE stocks (growth stocks).

vg

 

 

(Value – top line, growth, bottom line – we would make the difference in a long short strategy)

This has some advantages over the first technique, in that the stocks are otherwise likely to be similar in long and short legs, and hence the correlations should be high – thus the hedge from the short leg should work better. Also, this is the standard way in which academics document characteristics of stocks that affect future returns –  so there is a lot of literature and data easily available under this framework.

3. Going long something that’s “good” and being short the market. This is the most common way industry practitioners seem to run long short portfolios. Their long legs are driven by their proprietary research and secret signals but on the short side, they simply use the market. The real advantage to this is that from a practitioners perspective, shorting the market is much, much easier than shorting a collection of stocks. There is infinite liquidity in market indices and you never have to be worried about getting a locate.

These are just three possible ways to implement a long short strategy. Each with its own advantages and disadvantages. They are definitely psychologically useful when investing in markets that are at “all time highs,” but there’s no reason to restrict their use to such situations – they can be used any time you want to a hedge against potential large downturns in the markets.

 

The sky is falling … [but I’m not short]

With the Dow and other indices at record levels, there is no shortage of pundits out there warning of an impending correction, or worse. See, for example, http://money.cnn.com/2016/04/15/investing/stock-market-donald-trump-ted-cruz/ and http://thesovereigninvestor.com/exclusives/80-stock-market-crash-to-strike-in-2016/ .

Some of the fear mongers, unfortunately, have an ulterior motive for predicting doom and gloom. A number of advisers look at such predictions as free options – if there is a crash, they can sagely point to their warnings and say, “See, I called it.” Some can even monetize their call… raising funds as investors look to re-allocate their decimated portfolios to stem the bleeding. If there is no crash, well, no one will look back and call them out on their incorrect call.

To me, the real question is whether these prognosticators have their money where their mouth is. If they think a major crash is coming, are they short? Or at least in cash? If not, I find their warnings have little credibility. They might be right, they might be wrong – either way, they’re not betting their own money on the call.

As the famous saying from Paul Samuelson goes, Economists (using technical indicators), “predicted nine of the last five recessions.” It wouldn’t surprise me if unscrupulous financial advisers and nay-saying pundits predicted ninety.

Blending factors…. the problem with intersections

I have recently been working on an academic paper on using multiple factors to invest. This is a marked departure from most of my other academic work (which generally involves hedge fund data). This research is also directly relevant to my investing work. While the research itself is still ongoing and I am not ready to share the conclusions, I had a couple of insights on how difficult it is to combine factors that I’d share.

The technique I’ve been using to combine factors is looking for intersections – I believe value stocks outperform growth stocks and past winners outperform losers. I want to buy stocks that are both value stocks AND past winners. (Incidentally, there is a rigorous academic paper arguing for this exact factor combination by the managers of one of the most successful quantitative investing shops).

This works well… to an extent. The more factors you add, the fewer stocks will get through. As an example, if you wanted the top 10% of stocks by value (say P/E ratios) and the top 10% of stocks by past returns, and the two were uncorrelated, your filter would return about 1% of stocks in the universe. Adding a 3rd uncorrelated factor, say size (small cap firms generally outperform larger ones), would reduce the filtered stocks even further to about 0.1% of stocks in the universe.

Beyond 3 factors, it is impossible to use intersections to combine factors. The resulting sample size is simply too small. One could (and I have) relaxed the constraints on each individual constraint, and in that manner blend more factors, but this feels artificial and might even be to the detriment of the screen.

To use a sports analogy (and since the NBA championships are on), I could ask for the top 10% of 3 point shooters and top 10% of overall point scorers and I’d probably get Stephen Curry and a few others. If I then add top 10% of assists to my criteria, I probably won’t have a single player in the league fitting the bill. IF I then relax my criteria to be the top 30% of 3 point shooters, overall point scorers and assists, I’d probably get players in there again, but it’s unclear I’d like them over my original 2 factor criteria that returned Curry and co.

So intersections are tough to work with.

Value investing II

How to measure value?

There are many ways to measure value –

P/E

EV/EBIT or EV/EBITDA

P/B

replacement value multiples

However you measure it, value is designed to capture the idea that you’re “getting a deal.” P/E and EV/EBIT(DA) type measures reflect this by showing you how quickly you can earn your initial investment back …. A P/E of 20 means that each year you get 5% of your initial investment. A P/E of 3 you therefore mean that each year you get back 33% of your investment. Seems like a steal of a deal, right? 3 years and then it’s gravy. Unfortunately, most of the time, there is a reason that a P/E is 3 … specifically, markets anticipate that earnings are going to fall. If you look at companies with a 2-3 P/E – there are 7 of them below – you can see that in some cases (UAL, MTG, BPT), earnings have been falling. In another case, SDLP, there has been an unusually high earnings number in the recent quarter. For CBB, ARC and ESI, earnings are volatile. The one thing we don’t see for these 2-3 P/E companies is a consistently increasing earnings stream ….if so, it would be valued much higher.P/B is similar, but different. P/B and replacement value multiples, or multiples against reserves for commodity firms capture the deal you are getting on value – in this case, a low multiple may capture some hidden impairment of the assets of the firm. Perhaps the value reserves or machines are being marked to on the books is too high.

Ticker Company earnrecent earn1qago earn5qago
UAL United Continental 313,000,003.08 822,999,996.18 507,999,989.66
MTG MGIC Investment 69,191,000.28 102,418,001.99 133,075,997.27
CBB Cincinnati Bell 32,600,000.43 80,300,000.50 -18,299,999.74
SDLP Seadrill Partners 189,600,001.44 35,400,000.55 33,099,999.69
BPT BP Prudhoe Bay 15,043,999.77 31,508,000.06 43,378,000.73
ARC ARC Document Solutions 3,183,999.96 80,335,999.25 -2,327,000.01
ESI ITT Educational Services 10,446,999.86 1,688,000.00 14,917,000.10

 

Skimming through the list of companies with 10-20% Price to book ratios (the company trades at 10-20% of book equity), there are 13: half are oil and gas and hal fare financials … again situations where it’s easily possible for book value to be way too high (given the recent fall in the price of oil, oil and gas equipment may easily be worthless; and financial assets such as bad loans can also easily be worthless).

 

So there are good reasons why P/E and P/B type ratios can be low – on average, they seem unjustifiably so, as these firms, on average, outperform, but if you own these firms, be prepared for decreasing earnings, writedown of assets and other things that accompany low multiples.