4 Types, then a docstring

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

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.

A patch to src/tally/__init__.py.

In src/tally/__init__.py, the signature of count now says text: str, and -> dict[str, int] for what it gives back. The body is the same.

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.

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 diff of 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.

A patch to src/tally/__init__.py.

In src/tally/__init__.py, the first line of count is now its docstring. It says that count ignores case.

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

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

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 diff of 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.