Computing / Lesson 01
Procedures and state
Read programs as precise transformations of state, beginning with Python.
orient
Why this idea had to exist
Programming begins when an intention becomes a sequence another machine can execute without guessing. Tracing state makes that sequence inspectable and turns debugging into explanation rather than trial and error.
intuition
Build a picture you can reason with
Imagine a workbench with labeled cards. An assignment changes which value a label refers to. A function creates a temporary bench with inputs, performs a transformation, and returns a result. A loop repeats a controlled change until its rule says stop.
formalize
Give the intuition a precise edge
A program state maps names and locations to values. Assignment updates the state; expressions evaluate within it. Control flow selects the next instruction. A function defines a parameterized state transition and may return a value without exposing its local names.
work through
Follow the decisions, not just the symbols
Trace total=0 followed by a loop over [2,4,6] that adds each value. The states are 0→2→6→12. The crucial step is recording the old total and current item before applying the assignment.
experiment
Change one thing and watch the model answer
Step through a small Python trace one expression at a time. Predict the next state before revealing it, then change the input list and identify which instructions remain invariant.
retrieve
Close the page and reconstruct it
Answer before opening the explanation. Retrieval is evidence only when the answer is produced without a hint.
What information must a state trace record to explain an assignment?
It must record the relevant values before evaluation, the expression result, and the updated binding or location afterward.
transfer
Move the idea into a new setting
Write and trace a function that converts a sequence of temperatures from Celsius to Fahrenheit without mutating the input list.
reflect
Leave with a diagnostic habit
When code surprises you, slow time down. Write the state before and after the smallest instruction that changes it.
Source record
Follow the idea back.
- Reference
- The Python Tutorial
- Publisher
- Python Software Foundation
- License
- PSF License Version 2
- Accessed
- 2026-08-12
- URL
- https://docs.python.org/3/tutorial/