4 Types and a docstring

Build it yourself. Read the tutorial is the other way to read this part.

If you start at this part, make your clone as Get the project says, and then run this command. It puts in your clone the files that this part starts from. A file that the project deleted before this part stays, so delete it if git check lists it:

git rm -rq --cached --ignore-unmatch -- :/ && git restore --source 1568a522d233 --staged --worktree -- :/

This part is whole. It adds the types, then the docstring.

just setup

To learn what count takes and what it gives, a reader must now read its body. Its signature can say it at a glance, and an editor can check it. One line under the signature can say what the function does. Neither changes what count does, so the tests pass as before.

The code before this part. The code after it.

4.1 Types

The signature def count(text): does not say what text is, or what count gives back. Types say it. count takes a str, and gives a dict[str, int], a dictionary from words to counts. The body stays the same.

Apply the patch to src/tally/__init__.py, from the top of the project:

curl -fsSL https://github.com/rahuldave/tally/commit/a7606fcc89be70f26f75353333a506e9891a6ea1.diff | git apply --include=src/tally/__init__.py

The patch writes the signature of count again, with its types.

uv run python -m unittest discover -s tests -q

The three tests pass as before, because types change what the code says, not what it does.

Check your files against this move. The command prints nothing when they match, and otherwise shows what differs:

git check a7606fcc89be

If you are stuck, this command puts the files of this move in place of yours. A file that you made yourself stays:

git restore --source 1568a522d233 --staged -- :/ && git restore --source a7606fcc89be --staged --worktree -- :/

What changed

src/tally/__init__.py: the signature says what goes in and what comes out. 1 line added, 1 removed. The file.
- look at def count(text: str) -> dict[str, int]:

The patch to src/tally/__init__.py

@@ -3,7 +3,7 @@
 import sys
 
 
-def count(text):
+def count(text: str) -> dict[str, int]:
     counts = {}
     for word in text.lower().split():
         counts[word] = counts.get(word, 0) + 1

This change on GitHub. The code after it.

4.2 A docstring

The types say what count takes and gives, but not what it does with the text. A docstring says it. It is a string on the first line of a function. Python keeps it in count.__doc__, and help(count) prints it.

Apply the patch to src/tally/__init__.py, from the top of the project:

curl -fsSL https://github.com/rahuldave/tally/commit/f79588d3b046ec2787725cdb6e3fcf952014e078.diff | git apply --include=src/tally/__init__.py

The patch adds the docstring under the signature of count, before the line counts = {}.

uv run python -c "import tally; print(tally.count.__doc__)"

It prints the docstring, How many times each word of `text` appears, ignoring case.

count now says what it takes and what it gives, in its signature and in its docstring. Its body did not change.

Check your files against this move. The command prints nothing when they match, and otherwise shows what differs:

git check f79588d3b046

If you are stuck, this command puts the files of this move in place of yours. A file that you made yourself stays:

git restore --source a7606fcc89be --staged -- :/ && git restore --source f79588d3b046 --staged --worktree -- :/

What changed

src/tally/__init__.py: one line under the signature says what the function does. 1 line added. The file.
- look at "How many times each word of `text` appears, ignoring case."

The patch to src/tally/__init__.py

@@ -4,6 +4,7 @@ import sys
 
 
 def count(text: str) -> dict[str, int]:
+    "How many times each word of `text` appears, ignoring case."
     counts = {}
     for word in text.lower().split():
         counts[word] = counts.get(word, 0) + 1

This change on GitHub. The code after it.