Sample code for: Pyrefly: A Fast Static Type Checker for Python Projects

pyrefly-python/README.md

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+# Pyrefly: A Fast Static Type Checker for Python Projects
+
+This folder provides the code examples for the Real Python tutorial [Pyrefly: A Fast Static Type Checker for Python Projects](https://realpython.com/pyrefly-python/)

pyrefly-python/aggregations.py

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+from collections.abc import Iterable
+from typing import Any
+
+
+def average(numbers: list[int | float]) -> float:
+    if not numbers:
+        raise ValueError("average() requires at least one number")
+    return sum(numbers) / len(numbers)
+
+
+def median(values: Any, sort=False):
+    values = sorted(values) if sort else values
+    return values[(len(values) - 1) // 2]
+
+
+def count(values: Iterable[int | None]):
+    return sum(1 if v is not None else 0 for v in values)

pyrefly-python/collection_average.py

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+from collections.abc import Collection
+
+
+# A Collection is any object that has a length and can be iterated over
+def average(numbers: Collection[int | float]) -> float:
+    if not numbers:
+        raise ValueError("average() requires at least one number")
+    return sum(numbers) / len(numbers)
+
+
+average([1, 2.2, 3])
+average({1, 2.2, 3})
+average((1, 2.2, 3))

pyrefly-python/incorrect_types.py

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+def average(numbers: list[int | float]) -> float:
+    if not numbers:
+        raise ValueError("average() requires at least one number")
+    return sum(numbers) / len(numbers)
+
+
+average(["a", "b", "c"])
+average(["d", "e", "f"])

pyrefly-python/requirements.txt

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+pyrefly==1.2.0

pyrefly-python/untyped.py

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+def average(numbers):
+    if not numbers:
+        raise ValueError("average() requires at least one number")
+    return sum(numbers) / len(numbers)
+
+
+average([1, 2.2, 3])

pyrefly-python/untyped_inferred.py

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+def average(numbers: list[float | int]) -> float:
+    if not numbers:
+        raise ValueError("average() requires at least one number")
+    return sum(numbers) / len(numbers)
+
+
+average([1, 2.2, 3])