03 · Commits and the staging area

You fix a bug in count.py: "the" and "the," were counted as different words. While you're there, you add a usage line to the README. Those are two separate changes. If one turns out wrong you'll want to undo it alone, so each gets a commit of its own.

import re
import sys
from collections import Counter

text = open(sys.argv[1]).read().lower()
words = re.findall(r"[a-z']+", text)
print("words:", len(words))
for word, n in Counter(words).most_common(3):
    print(word, n)

$ git status --short
 M README.md
 M count.py
$ git diff README.md
diff --git a/README.md b/README.md
index 737ddaf..6cbb648 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,5 @@
 # textstats
 
 Count the words in a text file.
+
+Usage: python3 count.py notes.txt

$ git add count.py
$ git status --short
 M README.md
M  count.py
$ git commit -m "Ignore punctuation when counting"
[main 0f2361e] Ignore punctuation when counting
 1 file changed, 2 insertions(+), 1 deletion(-)
$ git add README.md
$ git commit -m "Show how to run it in the README"
[main ba52d05] Show how to run it in the README
 1 file changed, 2 insertions(+)

git add copies a file, as it is at that moment, into a holding area for the next commit. git commit saves what's in that area, and nothing else. So you decide what each commit holds, whatever else you've changed on disk. git diff --staged shows what's waiting there.

Read git status --short as two columns: the left one is the staging area, the right one the working tree. An M on the right is changed but not staged, an M on the left is staged, and ?? is untracked. A file can be in both columns at once, as the next question shows.

History is only worth keeping if you can read it. git log lists commits, newest first, and git show shows one in full.

$ git log --oneline
ba52d05 (HEAD -> main) Show how to run it in the README
0f2361e Ignore punctuation when counting
26f2494 Count words in a text file
$ git show --stat HEAD~1
commit 0f2361ebe6c44f6cfb3082886bafb79ca2a4a721
Author: Ana Lima <[email protected]>
Date:   Wed Nov 4 09:31:00 2026 +0000

    Ignore punctuation when counting

 count.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Each commit records the one before it, so history is a chain you walk back from HEAD. ~1 takes one step back and ~2 two. They work wherever git expects a commit: git diff HEAD~2 HEAD shows everything the last two commits changed.

A message is for whoever reads the history a year from now. The diff already shows what changed, so say what the commit does and why. Git's own manual suggests a first line of at most 50 characters, then a blank line and the details. git commit without -m opens your editor for exactly that.