In Python, if you want to specify a sequence of numbers from a up to (but excluding) b, you can write range(a, b). This generates the sequence a, a+1, a+2, ..., b-1. You start at a and keep going until the next number would be b.

In Python 3, range is lazy and the values in the sequence do not ma­te­ri­al­ize until you consume the range.

>>> range(3,12)
range(3, 12)
>>> list(range(3,12))
[3, 4, 5, 6, 7, 8, 9, 10, 11]

Trey Hunner makes the point that range is a lazy iterable rather than an iterator.

You can also step by an increment other than one: range(a, b, s). This generates a, a+s, a+2*s, ..., b-s (assuming that (b - …continue.

On 2nd February 1882, in the Dublin suburb of Rathgar, a son was given unto John and May Joyce. James Joyce celebrated his 40th birthday in Paris on 2nd February 1922 by receiving the first printed copy of his novel Ulysses. Parts of it had already been published in literary magazines and the book was eagerly received by the cognoscen­ti. It took more than a decade for Ulysses to be published in Britain and the United States. Censors had considered the book obscene, but the courts es­tab­lished that it had legitimate literary merit.

For decades, Ulysses was poorly received in Ireland. The book was considered blas­phe­mous and obscene by many. Worse, Joyce had …continue.

A while back, I had extracted some code out of a large file into a separate file and made some mod­i­fi­ca­tions. I wanted to check that the dif­fer­ences were minimal. Let’s say that the extracted code had been between lines 123 and 456 of large_old_­file.

diff -u <(sed -n '123,456p;457q' large_old_file) new_file

What’s happening here?

• sed -n '123,456p' is printing lines 123–456 of large_old_­file.
• The 457q tells sed to abandon the file at line 457. Otherwise, it will keep reading all the way to the end.
• The <(sed ...) is an example of process sub­sti­tu­tion. The output of the sed invocation becomes the first input of the diff command.

A similar example: Diff a Trans­formed …continue.

40 years ago this month, I sat down at a computer and wrote a program. (Or "programme", as I spelled it then.) It was the first time I had ever used a computer. Very few people had used computers in 1982, in Ireland or elsewhere.

What was the program? No idea. Just a few lines of AppleSoft Basic. But it was enough to get me hooked and change my life.

I still get a hit when a little bit of code unlocks in my brain. It’s quite addictive. There’s always more to learn and to see.

I wrote more about this in 2012: 30 Years of Pro­gram­ming.

At the beginning of 2021, prompted by Russell Crowe’s defense of Master and Commander, I began yet another re-read of the twenty Aubrey-Maturin novels. Or, as the fandom would have it, another cir­cum­nav­i­ga­tion. It’s probably my fifth or sixth cir­cum­nav­i­ga­tion, since I bought the complete boxed set as a Christmas present to myself in the early aughts.

I completed the twentieth book, Blue at the Mizzen, yesterday, and also the few pages of the final, unfinished novel, 21. (I also read about 120 other books in 2021, down from a stupendous 200 books in 2020, but that’s neither here nor there.)

I think I'm due for another re-read of Patrick O'Brian's Aubrey/Maturin novels (all …continue.

I’ve read hundreds of technical books over the last 40 years. Crafting In­ter­preters is an instant classic, and far more readable and fun than many of the classics.

Nystrom covers a lot of ground in this book, building two very different in­ter­preters for Lox, a small dynamic language of his own design. He takes us through every line of jlox, a Java-based tree-walk in­ter­preter, and of clox, a bytecode virtual machine written in C.

For the first im­ple­men­ta­tion, jlox, he covers such topics as scanning, parsing ex­pres­sions with recursive descent, evaluating ex­pres­sions, control flow, functions …continue.

I was surprised to read this evening that the Apache Web Server just fixed an actively exploited path traversal flaw.

🚨 Apache has disclosed an *actively exploited* Path traversal flaw in the #open­source "httpd" server. Over 112,000 exposed Apache servers run version 2.4.49, and should be upgraded now!
New fix checks for encoded path traversal characters e.g. /../.%2E/https://t.co/1tLNc3LAul pic.twitter.com/mDHLEU3k9N
— Ax Sharma (@Ax_Sharma) October 5, 2021

Apparently, it was introduced over a year ago.

I’m gobsmacked that Apache didn’t have a robust suite of tests for this.

Directory Traversal attacks have been a problem for web servers since the beginning. OWASP, PortSwig­ger, and Spanning all have ex­pla­na­tions that you can read. The essence is that you make a request …continue.

We had a per­for­mance regression in a test suite recently when the median test time jumped by two minutes.

We tracked it down to this (simplified) code fragment:

task_inclusions = [ some_collection_of_tasks() ]
invalid_tasks = [t.task_id() for t in airflow_tasks
                 if t.task_id() not in task_inclusions]

This looks fairly in­nocu­ous—and it was—until the size of the result returned from some_­col­lec­tion_of_­tasks() jumped from a few hundred to a few thousand.

The in comparison operator con­ve­nient­ly works with all of Python’s standard sequences and col­lec­tions, but its efficiency varies. For a list and other sequences, in must search linearly through all …continue.

I’ve been using password managers for at least 15 years to keep track of all my passwords. I have separate, distinct, strong passwords for hundreds of sites, and I’ve only memorized the handful that I need to actually type regularly.

I started out with the KeePass desktop app originally, but I switched to the online LastPass app about a decade ago. At work, we use 1Password.

When I register for a site, LastPass generates a random password for me, such as:

tV%5joS$U6^uY5xU
T2oEUY!g70Iv1b&I
8kNHg9*A5GMR9%8D

LastPass securely syncs my passwords between machines and devices. Its browser in­te­gra­tion and its Android and iPhone apps mean that I rarely ever have to actually type any of those ugly messes in.

But when …continue.

In The Punc­tu­a­tion Marks Loved (and Hated) by Famous Writers, Emily Temple relays a range of opinions from writers such as Tom Wolfe, Elmore Leonard, and Ursula K. Le Guin on periods, semicolons, hyphens and more.

On commas:

Listens to the sound of the sentence, and is always right, Bob: Toni Morrison

[On her editor, Bob Gottlieb, who famously “was always inserting commas into Morrison’s sentences and she was always taking them out”] We read the same way. We think the same way. He is over­whelm­ing­ly aggressive about commas and all sorts of things. He does not understand that commas are for pauses and breath. He thinks commas are for gram­mat­i­cal things. We have come to an …continue.