From c0ad3cee4d4819550295f031d9dde0c721377146 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Fri, 1 May 2026 17:01:14 -0500
Subject: [PATCH] Add Assert Is Only A Development Check as a Python TIL

---
 README.md                                    |  3 +-
 python/assert-is-only-a-development-check.md | 38 ++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 python/assert-is-only-a-development-check.md

diff --git a/README.md b/README.md
index bab0fc3..f1382be 100644
--- a/README.md
+++ b/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).
 
-_1781 TILs and counting..._
+_1782 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -1050,6 +1050,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Access Instance Variables](python/access-instance-variables.md)
 - [Access Most Recent Return Value In REPL](python/access-most-recent-return-value-in-repl.md)
 - [Access Variables Outside Loop Scope](python/access-variables-outside-loop-scope.md)
+- [Assert Is Only A Development Check](python/assert-is-only-a-development-check.md)
 - [Avoid Modification With Frozen Dataclass](python/avoid-modification-with-frozen-dataclass.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)
diff --git a/python/assert-is-only-a-development-check.md b/python/assert-is-only-a-development-check.md
new file mode 100644
index 0000000..359e7b0
--- /dev/null
+++ b/python/assert-is-only-a-development-check.md
@@ -0,0 +1,38 @@
+# Assert Is Only A Development Check
+
+The `assert` keyword is used in Python to write a statement that will check some
+assertion and raise an error if it isn't met. This is only meant to be used as a
+check during development because it can be easily optimized out of the code.
+
+```python
+stuff = None
+
+assert stuff, "We need to have some stuff to proceed"
+
+print(f"We have {stuff or 'something'}!")
+```
+
+If I execute this code with `python`, it will raise on that second line of code.
+
+```bash
+❯ python assert_example.py
+Traceback (most recent call last):
+  File "/Users/lastword/dev/jbranchaud/py-vmt/assert_example.py", line 3, in <module>
+    assert stuff, "We need to have some stuff to proceed"
+           ^^^^^
+AssertionError: We need to have some stuff to proceed
+```
+
+This `assert` statement will be stripped out of the compiled bytecode if the
+`-O` (capital o) flag is used. Notice how running the same file with that flag
+does not lead to an `AssertionError`.
+
+```python
+❯ python -O assert_example.py
+We have something!
+```
+
+If I want to make sanity checks for situations that would be caused by a bug in
+the code, an `assert` statement can be a good candidate. However, if I am making
+runtime checks like validating user input, then an `if` statement and raising
+something like a `ValueError` is better.