Add Force Remaining Arguments To Be Named as a Python TIL

README.md

@@ -10,7 +10,7 @@ working across different projects via [VisualMode](https://www.visualmode.dev/).
 
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-_1827 TILs and counting..._
+_1828 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -1083,6 +1083,7 @@ If you've learned something here, support my efforts writing daily TILs by
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+- [Force Remaining Arguments To Be Named](python/force-remaining-arguments-to-be-named.md)
 - [Get Absolute Seconds From `timedelta` Object](python/get-absolute-seconds-from-timedelta-object.md)
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python/force-remaining-arguments-to-be-named.md

@@ -0,0 +1,61 @@
+# Force Remaining Arguments To Be Named
+
+When the _positional argument collector_ (`*`) is used in a function definition,
+all the arguments that follow it must now be explicitly named when invoking that
+function. This is regardless of whether you are collecting positional arguments
+into a named tuple (e.g. `*rest`) or are using the empty/dummy version (`*`).
+
+A friend recently recommended I use this syntax to force some configuration
+values (often booleans) to be explicitly named at call sites.
+
+Here is an example of this in my [`py-vmt` project](https://github.com/jbranchaud/py-vmt):
+
+```python
+class CliContext:
+    def __init__(self, *, verbose: bool, repo: SessionRepository | None = None) -> None:
+        self.verbose: bool = verbose
+        self.active_session: Session | None = None
+        self.repo: SessionRepository = repo or JsonRepository()
+        self.active_session = self.repo.active_session()
+```
+
+Notice that right after `self` is the `*` which means that both `verbose` and
+`repo` must be named arguments.
+
+Here is a corresponding call site:
+
+```python
+    ctx.obj = CliContext(verbose=True)
+```
+
+Now when I initialize `CliContext`, there is no choice for me to pass in an
+unnamed argument of `True`. It has to be paired with `verbose`. Above I've
+excluded `repo` because that falls back to a default value. If I were to include
+it, it would have to be named.
+
+The same applies to this scenario where I'm collecting the positional arguments.
+
+```python
+def build_identifier(first, *rest, delimiter="/"):
+    if rest is None:
+        return first
+
+    return delimiter.join([first, *rest])
+```
+
+```python
+>>> print(build_identifier("taco"))
+taco
+>>> print(build_identifier("taco", "bell", "mas", delimiter="-"))
+taco-bell-mas
+>>> print(build_identifier("taco", "bell", "mas", "-"))
+taco/bell/mas/-
+```
+
+Notice in the third example where I don't use a named argument for the
+delimiter. It instead gets swept up in the collection of positional arguments.
+
+This language of _positional argument collector_ I got from [Python in a
+Nutshell, 4th
+Edition](https://www.oreilly.com/library/view/python-in-a/9781098113544/) (see
+pg. 96).