Add Iterate Over A Dictionary as a Python TIL

README.md

@@ -10,7 +10,7 @@ working across different projects via [VisualMode](https://www.visualmode.dev/).
 
 For a steady stream of TILs, [sign up for my newsletter](https://visualmode.kit.com/newsletter).
 
-_1743 TILs and counting..._
+_1751 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -29,6 +29,7 @@ If you've learned something here, support my efforts writing daily TILs by
 * [Ansible](#ansible)
 * [Astro](#astro)
 * [AWS](#aws)
+* [Bash](#bash)
 * [Brew](#brew)
 * [Chrome](#chrome)
 * [Claude Code](#claude-code)
@@ -126,6 +127,10 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Turn Off Output Pager For A Command](aws/turn-off-output-pager-for-a-command.md)
 - [Use Specific AWS Profile With CLI](aws/use-specific-aws-profile-with-cli.md)
 
+### Bash
+
+- [Edit The Current Command Prompt](bash/edit-the-current-command-prompt.md)
+
 ### Brew
 
 - [Clean Up Your Brew Installations](brew/clean-up-your-brew-installations.md)
@@ -241,6 +246,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Reload The nginx Configuration](devops/reload-the-nginx-configuration.md)
 - [Resolve The Public IP Of A URL](devops/resolve-the-public-ip-of-a-url.md)
 - [Running Out Of inode Space](devops/running-out-of-inode-space.md)
+- [Set, Get, And Unset Env Vars With Dokku](devops/set-get-and-unset-env-vars-with-dokku.md)
 - [Set Up Domain For Hatchbox Rails App](devops/set-up-domain-for-hatchbox-rails-app.md)
 - [SSH Into A Docker Container](devops/ssh-into-a-docker-container.md)
 - [SSL Certificates Can Cover Multiple Domains](devops/ssl-certificates-can-cover-multiple-domains.md)
@@ -1033,12 +1039,16 @@ If you've learned something here, support my efforts writing daily TILs by
 ### Python
 
 - [Access Instance Variables](python/access-instance-variables.md)
+- [Access Most Recent Return Value In REPL](python/access-most-recent-return-value-in-repl.md)
 - [Break Debugger On First Line Of Program](python/break-debugger-on-first-line-of-program.md)
 - [Check If Package Is Installed With Pip](python/check-if-package-is-installed-with-pip.md)
 - [Create A Dummy DataFrame In Pandas](python/create-a-dummy-dataframe-in-pandas.md)
 - [Dunder Methods](python/dunder-methods.md)
+- [Easy Key-Value Aggregates With defaultdict](python/easy-key-value-aggregates-with-defaultdict.md)
 - [Install With PIP For Specific Interpreter](python/install-with-pip-for-specific-interpreter.md)
 - [Iterate First N Items From Enumerable](python/iterate-first-n-items-from-enumerable.md)
+- [Iterate Over A Dictionary](python/iterate-over-a-dictionary.md)
+- [Keep A Tally With collections.Counter](python/keep-a-tally-with-collections-counter.md)
 - [Load A File Into The Python REPL](python/load-a-file-into-the-python-repl.md)
 - [Override The Boolean Context Of A Class](python/override-the-boolean-context-of-a-class.md)
 - [Store And Access Immutable Data In A Tuple](python/store-and-access-immutable-data-in-a-tuple.md)
@@ -1639,6 +1649,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Check The Current Working Directory](unix/check-the-current-working-directory.md)
 - [Check The Installed OpenSSL Version](unix/check-the-installed-openssl-version.md)
 - [Clear The Screen](unix/clear-the-screen.md)
+- [Combine All My TILs Into A Single File](unix/combine-all-my-tils-into-a-single-file.md)
 - [Command Line Length Limitations](unix/command-line-length-limitations.md)
 - [Compare Two Variables In A Bash Script](unix/compare-two-variables-in-a-bash-script.md)
 - [Configure cd To Behave Like pushd In Zsh](unix/configure-cd-to-behave-like-pushd-in-zsh.md)
@@ -1710,6 +1721,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Ignore A Directory During ripgrep Search](unix/ignore-a-directory-during-ripgrep-search.md)
 - [Ignore The Alias When Running A Command](unix/ignore-the-alias-when-running-a-command.md)
 - [Include Ignore Files In Ripgrep Search](unix/include-ignore-files-in-ripgrep-search.md)
+- [Inspect EXIF Data For An Image File](unix/inspect-exif-data-for-an-image-file.md)
 - [Interactively Browse Available Node Versions](unix/interactively-browse-availabile-node-versions.md)
 - [Interactively Switch asdf Package Versions](unix/interactively-switch-asdf-package-versions.md)
 - [Interpret Cron Schedule From The CLI](unix/interpret-cron-schedule-from-the-cli.md)

bash/edit-the-current-command-prompt.md

@@ -0,0 +1,18 @@
+# Edit The Current Command Prompt
+
+A neat feature of `bash` is the ability to open whatever the current state of
+the command prompt is into your default editor.
+
+Let's say we have a really long command that we've just tried to run, but it
+failed and we need to make a small change somewhere in the middle. Instead of
+holding the left arrow key for 30 seconds, we can instead hit `CTRL-X CTRL-E`.
+
+This pops us into our `EDITOR` (or maybe `VISUAL`, not sure which). In my case,
+that is `nvim`. I now have access to all the features I'm used to in `nvim` for
+quickly navigating to and editing, searching and replacing, or whatever.
+
+Once I've got the command how I like it, I can save and exit (`:wq`) and the
+updated command will be executed.
+
+This is similar to [the `fc` builtin](unix/fix-previous-command-with-fc.md),
+which also happens to be available for `zsh`.

devops/set-get-and-unset-env-vars-with-dokku.md

@@ -0,0 +1,29 @@
+# Set, Get, And Unset Env Vars With Dokku
+
+The `dokku` CLI provides `config` subcommands for managing environment variables
+for the target container.
+
+An env var can be set for an active container with `config:set`:
+
+```bash
+$ dokku config:set app-name JEMALLOC_ENABLED=true MALLOC_CONF="stats_print:true"
+```
+
+Notice I'm able to set multiple env vars at once if needed.
+
+If I ever need to check what an env var is currently set to for one of my app
+containers, I can use `config:get`:
+
+```bash
+$ dokku config:get app-name JEMALLOC_ENABLED
+true
+```
+
+I can always override any value with another `config:set`. However, if I need to
+entirely remove the env var, I can use `config:unset`:
+
+```bash
+$ dokku config:unset app-name MALLOC_CONF
+```
+
+[source](https://dokku.com/docs/configuration/environment-variables/)

python/access-most-recent-return-value-in-repl.md

@@ -0,0 +1,34 @@
+# Access Most Recent Return Value In REPL
+
+One of my favorite features of Ruby's `irb` and `pry` are that you can use `_`
+to reference the most recent return value. Often as we use an interpreter or
+REPL, we end up with _intermediate_ values. That is, we've execute some kind of
+statement which returned a value and we now want to use that resulting value in
+our next statement. Python also supports `_`.
+
+Let's say I've run a statement that took a while to process, but I forgot to
+assign it to a variable. Instead of re-running the whole thing, I can create a
+variable that references the previous return value using `_`.
+
+```python
+>>> BytePairEncoding.train_bpe(long_text)
+{'merge_rules': [...], 'vocab': {...}}
+>>> result = _
+>>> list(result.keys())
+['merge_rules', 'vocab']
+```
+
+Even if I don't necessarily want to assign it a variable, it can be nice to
+reference the previous value as I continue with what I'm doing:
+
+```python
+>>> result['merge_rules'][0][1]
+256
+>>> result['vocab'][_]
+b'e '
+```
+
+Notice how the value from the first statement gets used as part of a `dict`
+access.
+
+[source](https://docs.python.org/3/tutorial/introduction.html#numbers)

python/easy-key-value-aggregates-with-defaultdict.md

@@ -0,0 +1,53 @@
+# Easy Key-Value Aggregates With defaultdict
+
+The `collections` module has the `defaultdict` object that can be used to
+aggregate values tied to a key. What sets this apart from simply using a `dict`
+is that we get the base value for free. So if our aggregate value is a list,
+then we get `[]` by default for each new key. In the same way, we'd get `0` if
+it was constructed with `int`.
+
+Here is the counter example from [Keep A Tally With
+collections.Counter](keep-a-tally-with-collections-counter.md)
+
+```python
+from collections import defaultdict
+
+def get_pair_counts(token_ids: list[int]) -> Counter:
+    """Count how often each adjacent pair appears"""
+    counts = defaultdict(int)
+    for i in range(len(token_ids) - 1):
+        pair = (token_ids[i], token_ids[i + 1])
+        counts[pair] += 1
+    return counts
+```
+
+We never have to initially set a key to `0`. If the key is not yet present, then
+`int()` (the zero-value constructor) is used as the `__missing__` value.
+
+We can do the same with `list`:
+
+```python
+>>> import collections
+>>> stuff = collections.defaultdict(list)
+>>> stuff['alpha'].append(1)
+>>> stuff['alpha']
+[1]
+>>> stuff['beta']
+[]
+```
+
+In the same way, this uses `list()` as the `__missing__` value to start of each
+key with an `[]`.
+
+I find this so handy because in other languages I've typically had to do
+something more like this:
+
+```python
+words_by_length = {}
+for item in items:
+    if len(item) not in words_by_length:
+        words_by_length[len(item)] = []
+    words_by_length[len(item)].append(item)
+```
+
+This is much clunkier.

python/iterate-over-a-dictionary.md

@@ -0,0 +1,34 @@
+# Iterate Over A Dictionary
+
+Let's say we have a `dict` that contains counts of occurrences for each word in
+some sample text:
+
+```python
+words_frequency = {
+    "the": 4,
+    "a": 3,
+    "dog": 1,
+    "bone": 1,
+    "wants": 1,
+    ...
+}
+```
+
+Here is how we can iterate over the `dict`, accessing both the keys and values:
+
+```python
+for word, count in word_frequency.items():
+    print(f"- {word} appears {count} time{'' if count == 1 else 's'}")
+```
+
+Using the
+[`items()`](https://docs.python.org/3/library/stdtypes.html#dict.items) method,
+we're able to access both _key_ and _value_ with the for loop as it iterates.
+
+Another approach is to loop directly on the `dict` which implicitly surfaces the
+_key_ for iteration. This can then be used to get the value from the `dict`:
+
+```python
+for word in word_frequency:
+    print(f"- {word}: {word_frequency[word]}
+```

python/keep-a-tally-with-collections-counter.md

@@ -0,0 +1,40 @@
+# Keep A Tally With collections.Counter
+
+Python's `collections` module comes with a
+[`Counter`](https://docs.python.org/3/library/collections.html#collections.Counter)
+object which is a specialized dict subclass focussed on tallying counts of keys.
+
+> It is a collection where elements are stored as dictionary keys and their
+> counts are stored as dictionary values. Counts are allowed to be any integer
+> value including zero or negative counts.
+
+I used it recently while doing an exploratory implementation of a Byte-Pair
+Encoding (BPE):
+
+```python
+from collections import Counter
+
+def get_pair_counts(token_ids: list[int]) -> Counter:
+    """Count how often each adjacent pair appears"""
+    counts = Counter()
+    for i in range(len(token_ids) - 1):
+        pair = (token_ids[i], token_ids[i + 1])
+        counts[pair] += 1
+    return counts
+```
+
+Here I'm able to count the number of occurrences of each pair of bytes from the
+input text. A tuple of `int` values is hashable, so they work great as keys for
+a `Counter`.
+
+The count value of any key will default to `0`. That makes it straightforward to
+increment from there as you iterating over occurrences.
+
+```python
+>>> counts = Counter()
+>>> counts['hello']
+0
+>>> count['hello'] += 1
+>>> count['hello']
+1
+```

unix/combine-all-my-tils-into-a-single-file.md

@@ -0,0 +1,35 @@
+# Combine All My TILs Into A Single File
+
+In [Build A Small Text-based Training
+Dataset](https://www.visualmode.dev/build-a-small-text-training-dataset), I went
+over my need for a sizeable and interesting corpus of text that I could use as a
+training dataset I could use to run against [my own naive Byte Pair Encoding
+implementation](https://github.com/jbranchaud/build-an-llm-from-scratch/blob/main/chapter-02/bpe_tokenizer.py).
+My repo of hand-written TILs is a great candidate, but I need those smashed all
+into one file.
+
+Here is a formatted version of the one-liner I ended up with:
+
+```bash
+{
+  cat README.md; \
+  find */ -name '*.md' -print0 \
+  | sort -z \
+  | xargs -0 -I{} sh -c 'echo "<|endoftext|>"; cat "$1"' _ {}; \
+} > combined.md
+```
+
+This combines all 1700+ of my TILs into a single file separated by the
+`<|endoftext|>` delimiter.
+
+The two things I find most interesting about this command are:
+
+1. The use of a null byte (`\0`) separator between the filenames in case there
+   is anything weird (like spaces) in those filenames. This starts with
+   `-print0`. The `-z` of `sort` maintains that null byte separator. And then
+   `xargs` knows to handle it by the `-0` flag.
+
+2. We can coerce `xargs` into running multiple commands by having it spawn a
+   single shell process that runs each of those commands. To reliably pass the
+   filename into that shell process, we have `xargs` constitute it as the second
+   argument (`$1`) by substituting in the filename where `{}` appears.

unix/inspect-exif-data-for-an-image-file.md

@@ -0,0 +1,47 @@
+# Inspect EXIF Data For An Image File
+
+The `exiftool` CLI (which can be downloaded via `brew`) is a useful tool for
+inspecting all the EXIF data attached to a media file. A media file like an
+image has a bunch of additional details embedded in it like timestamps, image
+metadata, and sometimes location information.
+
+Here is all the data attached to a screenshot I found on my desktop:
+
+```bash
+❯ exiftool ~/Desktop/CleanShot\ 2025-11-17\ at\ 11.22.18@2x.png
+ExifTool Version Number         : 13.50
+File Name                       : CleanShot 2025-11-17 at 11.22.18@2x.png
+Directory                       : /Users/lastword/Desktop
+File Size                       : 1194 kB
+File Modification Date/Time     : 2025:11:17 11:22:21-06:00
+File Access Date/Time           : 2025:12:15 10:43:55-06:00
+File Inode Change Date/Time     : 2025:12:05 15:37:48-06:00
+File Permissions                : -rw-r--r--
+File Type                       : PNG
+File Type Extension             : png
+MIME Type                       : image/png
+Image Width                     : 2502
+Image Height                    : 1232
+Bit Depth                       : 8
+Color Type                      : RGB with Alpha
+Compression                     : Deflate/Inflate
+Filter                          : Adaptive
+Interlace                       : Noninterlaced
+XMP Toolkit                     : XMP Core 6.0.0
+Y Resolution                    : 144
+Resolution Unit                 : inches
+X Resolution                    : 144
+Exif Image Width                : 2502
+Color Space                     : sRGB
+User Comment                    : Screenshot
+Exif Image Height               : 1232
+SRGB Rendering                  : Perceptual
+Image Size                      : 2502x1232
+Megapixels                      : 3.1
+```
+
+This works with other kinds of media files. For instance, I ran this against an
+MP4 screen recording file which contained even more metadata.
+
+In addition to reading data, `exiftool` can also write it. See `man exiftool`
+for more details on what else it can do.