Debugging the Missing Time Spread Backtrades (Part 3)

I will continue with the debug journey after explaining the complexity of date formats.

As discussed near the end of this post, the date field is in “number of days since Jan 1, 1970.” Although unreadable on its own, I keep this format to check the data file. This can also be subtracted to get difference in days.

While the Python in the link converts these dates to a common format, I have also needed to convert in reverse. I came up with the following for this purpose, which [I think] needs time and datetime modules to work:

      int( time.mktime ( datetime.datetime.strptime ( summary_results [ “Trade End” ].iloc [ -4 ], \
      “%Y-%m-%d” ) . timetuple ( ) ) / 86400 )

The code takes YYYY-mm-dd as input and outputs days since 1/1/70. I also started to log row numbers in btstats to better identify what rows are matching should I need to refer back to the data file.

I think I am better prepared to approach this debug now that I can convert date forward and backward.

Let’s return to the end of Part 2 where I discovered no apparent problem is being had with the number of matching options.

My next thought was that maybe the particular spread is not being selected from the encoded data. I therefore moved the debug line just below the block where short option variables get assigned:

     for i in range ( len ( dte_list ) ):
         if dte_list[ i ] >= ( 30 * mte ):

Again, dates_without_enough_matches is empty. So far, things are seeming to work just fine when I know they’re not.

I then added these lines near the top before the conditional block begins to determine control branch:

    if current_date != current_date_prev: #debug
        print ( f ‘ current_date is { current_date }, common date is { datetime.utcfromtimestamp ( current_date * \
        86400 ).strftime( “%Y-%m-%d” ) }, trade status is { trade_status }, and control flag is { control_flag } . ‘ )
        current_date_prev = current_date

The idea here is to print out a trace line every time current_date changes (and to update current_date_prev to current_date).

Take a close look at two anomalies that stick out in the following output segment:

First, I am not sure why I get the occasional blank line as indicated by the red arrow. Current date is always five digits, common date is always the same format, trade_status is at most nine characters, and control_flag is always 11 characters. I get roughly 3500 total trace lines (from 2007 through 2021). In case the trace may occasionally exceed one line in length (thereby showing up as a blank second line), I added ‘123456789’ to the end expecting that I might see many more blanks (or second lines with some of those extra digits). This has no effect; the output looks the same.

While the first anomaly remains unresolved, the second anomaly (yellow) is more relevant. Per this this fourth-to-last paragraph, I am getting some consecutive trace lines printing out with ‘INCEPTION,’ which may indicate missing trade dates. 26 days are skipped from 2010-04-08 to 2010-05-04, though, when I would expect a trace line for each date in the data file.

What is going on here?

Debugging the Missing Time Spread Backtrades (Part 2)

By way of review, the idea is to log relevant variables in places where spreads could or should be found and aren’t. I left off discussing where in the program I need to insert code to do this.

In case I want to log in the ‘find_spread’ branch, let’s review the sub-branches:

• if int(float(stats[2])) > 200:
  I don’t want time spreads with options > 200 DTE. Skipping these rows is expected and no reason to log variables.
• elif len(dte_list) == 0 and if int(float(stats[6])) % 25 == 0 and if int(float(stats[6])) > float(stats[3]) and int(float(stats[6])) – float(stats[3]) < 26:
  This sub-branch appends data for the option with first matching strike price. It’s always possible that no match will be found in any row for a particular historical date, which to me would suggest an incomplete data file.
• elif int(float(stats[2])) == dte_list[0]: continue
  This skips rows [on same current_date and] with DTE equal to a previously-matched DTE. Nothing to log here.
• elif int(float(stats[1])) == current_date and if int(float(stats[6])) == strike_price:
  This sub-branch records DTE for subsequent strike price matches. The different DTE represents a different expiration month. If the previously-matched strike price is not matched here, then it may be evidence of an incomplete data file.
• else:
  This sub-branch should be executed only after the program has gone through all options on current_date. If no spread has been found, then a skipped trading day will result and len(dte_list) should be < 2. Alternatively, a found spread(s) may not selected in this sub-branch. Either way, logging relevant variables here seems to make good sense.

What are the relevant variables to log?

I increasingly suspect len(dte_list) should be looked at first. On any given day it should be > 2 for at least two matching options (one potential spread). As a first attempt, I will append current_date to a new list dates_without_enough_matches at the top of the ‘find_spread’ ELSE sub-branch for any day that does not meet this criterion.

Surprisingly, the list is empty! This suggests failure to match strike price is not the issue.

Just to be transparent, I am now moving the following line to the end of the ‘find_spread’ ELSE sub-branch:

      current_date = int(float(stats[1])) #updating

Since the previous elif executes on the same current_date (and strike price match), by implication this sub-branch takes place on the next day. Updating current_date at the beginning of this sub-branch forced me to use “current_date – 1” in following lines, which may not be accurate in case of weekends, holidays, etc. Updating at the end eliminates this problem. While not part of the current debugging effort, in scrutinizing this part of the program I saw opportunity for improvement.

I will continue next time.

Debugging the Missing Time Spread Backtrades (Part 1)

Because the current debugging effort is challenging, today I want to put my thoughts to computer screen and push forward to find out why the backtester is missing trades (last discussed here).

Need some juice today? Let’s get in the mood with this (thanks Frida!).

The first thing I should do is run the backtest a couple more times to make sure the values from the table in the previous post are repeatable. I would be more concerned if trades get missed randomly than regularly.

Next, I want to know the values of all relevant variables when trade skipping takes place. I can then trace what I expect should be the logic through the program to see if the results actually match.

Relevant variables can be monitored in one of two ways.

First, I can create a variable containing current_date minus previous trade ending date and raise an exception > 5. This would limit study to one case at a time, which should be sufficient if the cause of missing trades is uniform. Going this route, I need to write the dataframes to .csv and file.close() before raising an exception, which will immediately halt the program. The former will allow me to view the entire dataframe in Excel, which is easier than viewing with Jupyter Notebook. file.close() will avoid the annoying “file in use” warning when I try to open the file after an exception has been raised.

The second way to monitor relevant variables is to let the program run all the way through and collect data on the variables for every trading day without a position. Going this route, I can add code to write to btstats per usual. Skipped days would be evident as consecutive rows labeled ‘INCEPTION.’ I can also scroll down to the particular dates I anticipate this to occur, where I would expect to see mostly zeros with all variables reset.

I’m not sure btstats contains all the relevant variables I want to monitor, which I need to think carefully about to determine. Should this be true, I can always create another dataframe with relevant variables as column names.

The next thing I need to figure out is where in the program I need to call for the relevant variables to be logged. I feel confident to say it should come when control_flag is ‘find_spread.’ That is, after all, when the program is iterating through days without any positions. I also think it makes sense to log relevant variables when spread legs are not encoded.

I will continue next time.

Final Word on Formatting Datetime Axes

Today I will pick up plotting datetimes with uniform tick labels.

I’ve learned this is not as difficult as I may* have suspected. The x-coordinates are given in trade_list, which is a list of strings. I need datetimes, which can be created like this:

      trade_dates_as_datetime = [datetime.strptime(i, “%Y-%m-%d”) for i in trade_list]

Alternatively, I can ago back to pd.date_range() (introduced here) and include the first/last [string] dates from trade_list:

As mentioned in that earlier post, these x-values are type pd.Timestamp, which I believe is a datetime.

One thing I don’t like is the first major tick printing after the first point. I can remedy with the following:

L5 prints major ticks at months 1 and 7. The first (last) major tick is the one preceding (following) the first (last) data point at 2006-07 (2021-08). This is default and leaves ample room to be aesthetically pleasing.

L6 prints minor ticks every month. If so desired, I could specify particular months by including them as a list (e.g. [4,10] would place a minor tick at the other two quarters).

Interestingly, if I put bymonth=(2,6) in L5, then I get something looking like the nasty asymmetry seen in this lower plot:

This asymmetry is with major ticks plotted at the same months, though, whereas the earlier one results from major ticks being plotted on the first and 22nd of every month.

With L7 allowing me to adjust rotation, I can now customize about everything I would want on this graph.

Oh—what if I want to put a three-letter month instead of number? I can add this line:

      axs.xaxis.set_major_formatter(mdates.DateFormatter(‘%b-%Y’))

Editing rotation to 45 [degrees] produces this:

* — “May” because this has confused and led me in a complete circle to find a complete solution.

Backtester Development (Part 10)

I stumbled upon a couple further bugs in the second half of this post. Today I want to at least get started on the first one.

All of this started with the graph below and the highlighted point:

In looking to verify that [locally outlying] trade price, I expected to find early Apr 2013. In fact, the trade in question begins on Jun 21, 2013. Alarmed by the discrepancy, I suspected although the graph appears okay being packed with 255 points (trades), a closer look may reveal the points to be misaligned with dates.

Before going any further, I really should have checked to see if this is true (it is). Let’s do that right now:

I added a green, vertical line with MS Paint and calculated the distance between the green line and the previous vertical grid line (3-10-2013) as a fraction of the distance from the previous and following (12-17-2013) vertical grid lines. The fraction is 0.208, which places the date at May 5, 2013. The point is off by 47 days. That may not be much for a graph that spans over 14 years, but I thought computers didn’t make mistakes?!

It then occurred to me that while successfully getting the x-axis tick labels horizontally spaced, the points on the graph are also uniform even though the intervals between dates are not.

Once again, before going any farther I should have checked to see if this is true. Look closer at the second graph. Does the horizontal spacing look even to you? To me it doesn’t, but how can I verify?

I could do something like this:

      P_price_orig_zeroes = [ 0 for i in P_price_orig_all ]
      axs[1] . plot ( trade_list, P_price_orig_zeroes, marker=’o’, color=’g’ )

This creates a shadow line to the orange with equal x-values but all y-values set to zero:

Along the green line at the bottom, I have highlighted in yellow (punctuated by a few red arrows in case the highlighting is unclear) where the points are farther apart and the green line exposed.

As it turns out, the points do not align with dates but the horizontal spacing is not uniform, either. I now suspect the latter is due to the second bug I mentioned in the link from the first paragraph.

With regard to a possible cause for the irregular spacing, the code uses ax.set_xticks(). This is similar to plt.xticks() for which I included some documentation here. Looking closely at the former:

This establishes a list of strings as tick labels. Failure of the points to correctly align with label values (dates) makes sense for arbitrary strings as opposed to meaningful datetime objects. For correct alignment, maybe I can’t use ax.set_xticks() at all.

I want to correctly plot datetimes, but I want uniform tick labels rather than labels only where x-coordinates exist to match.

How can I make that happen?

Backtester Development (Part 9)

Today I want to finish updating what I have for backtester logic beginning with other considerations regarding maximum excursion (ME; see end of Part 8).

I’m not convinced that I need to report ME in btstats. As the statistic itself refers to an intratrade value, I can only think of two reasons to include it in the intraday report: to see how it changes over the course of the trade, which doesn’t matter to me, or to see exactly when it occurs, which I know anyway because I store that number separately ( _dte). All the context I probably need is in summary_results where I will also see initial DTE and DIT.

Besides, comparing ME across trades is easy in summary_results but much more difficult in btstats. In the former, each row corresponds to one trade and looking at ME across trades is as simple as scanning from row to row. In the latter, multiple rows correspond to each trade and I would need to do a lot of scrolling and looking up ‘WINNER’ or ‘LOSER’ in trade_status.

Removing ME from btstats will simplify an if-elif-else to if-else since ‘WINNER’ and ‘LOSER’ are otherwise handled the same.

And if trade_status is ‘WINNER’ or ‘LOSER,’ then before continuing data file iteration the program proceeds to:

• Assign ‘INCEPTION’ to trade_status
• Assign ‘find_spread’ to control_flag
• Reset all variables (fifth-to-last paragraph of Part 7 aside)
• Assign True to wait_until_next_day

I added a profit factor calculation to summary_results by:

• Appending two more rows (dictionaries) for mean and count of wins and losses by doing
  summary_results = summary_results.append ( { } ) [not just summary_results.append()]
• Calculating PF_calc by using .iloc[ ] to look up particular values
• Appending a row at the bottom to display PF_calc

Finally, I once again had to debug the graphing portion having to do with the x-axis tick labels that I discussed here, here, here, and here. I end up resolving this with three lines:

     L1: xtick_labels = pd.date_range (btstats [‘Date’] . iloc[0], btstats [‘Date’] . iloc[-1] , 20 )

This creates a list of 20 evenly-spaced trading dates including the first and last.

     L2: xtick_labels_converted = xtick_labels . strftime ( ‘%Y-%m-%d’ )

This is needed to avoid ConversionError [“Failed to convert value(s) to axis units”] from L3.

     L3: axs[0] . set_xticks (list (np . linspace (1, len (btstats . index), num = \
           len (xtick_labels_converted) ) ), xtick_labels_converted, rotation = 45)

This plots the evenly-spaced date labels at evenly spaced locations on the x-axis.

Technically speaking—and these are the details on which I get hung up and confused as a beginner—pd.date_range() in L1 returns a Datetimeindex. How do we know that and what does it mean?

I can do an internet search for pd.date_range:

I can do an internet search for datetime index:

Is “ndarray-like” bad English? An internet search turns up a page that explains this, too.

Ndarray can also be better understood by an internet search:

I don’t know much about arrays yet, but I do know they are a different data type from what [an internet search has informed me that] ax.set_xticks() is expecting:

Type str[ing] rather than [type] array or Index is expected. The Datetimeindex has large integers that nobody would want to see as tick labels anyway. L2 converts those to strings with a familiar character format (YYYY-MM-DD).

That pretty much covers the updated logic for this version of the backtester.