Modules, packages, and virtual environments
By the end of today you can explain what happens when Python runs an import, why the same code works on one machine and fails on another, and what a virtual environment actually isolates.
YesterdayOn Day 8 you learned that a command is found by searching PATH. An import works the same way, searching a path for modules.
TomorrowTomorrow you version the code itself, so you can move backwards as well as forwards.
Why this matters
Dependency confusion wastes more beginner hours than any other single thing. The isolation idea you meet today is exactly what a container does on Day 50, at a larger scale.
- Modules and imports
- Packages and dependencies
- Virtual environments
- Pinning dependencies
Learn it
70 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
4 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
40 minCreate two separate project directories, each with its own virtual environment, and install a different version of the same library in each. Prove they do not interfere by printing the installed version from inside each. Then freeze one to a requirements file, delete the environment, and rebuild it from that file.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
4 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01A module is a file; importing it executes it once and caches it
- 02Python finds modules along sys.path, much as the shell finds programs on PATH
- 03A virtual environment is a directory plus a PATH change, not magic
- 04Pinning is what makes 'it worked yesterday' a checkable claim
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.