78 lines
2.5 KiB
ReStructuredText
78 lines
2.5 KiB
ReStructuredText
Sample code for Chapter 10 - "Design patterns with first class functions"
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From the book "Fluent Python" by Luciano Ramalho (O'Reilly, 2015)
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http://shop.oreilly.com/product/0636920032519.do
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Notes
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=====
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No issues on file with zero type hints
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--------------------------------------
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Running Mypy on ``classic_strategy.py`` from the first edition, with no
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type hints::
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$ mypy classic_strategy.py
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Success: no issues found in 1 source file
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Type inference at play
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----------------------
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When the ``Order.due`` method made first assignment to discount as ``discount = 0``,
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Mypy complained::
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mypy classic_strategy.py
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classic_strategy.py:68: error: Incompatible types in assignment (expression has type "float", variable has type "int")
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Found 1 error in 1 file (checked 1 source file)
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To fix it, I made the first assigment as ``discount = 0``.
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I never explicitly declared a type for ``discount``.
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Mypy ignores functions with no annotations
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------------------------------------------
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Mypy did not raise any issues with this test case::
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def test_bulk_item_promo_with_discount(customer_fidelity_0):
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cart = [LineItem('banana', 30, .5),
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LineItem('apple', 10, 1.5)]
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order = Order(customer_fidelity_0, 10, BulkItemPromo())
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assert order.total() == 30.0
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assert order.due() == 28.5
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The second argument to ``Order`` is declared as ``Sequence[LineItem]``.
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Mypy only checks the body of a function the signature as at least one annotation,
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like this::
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def test_bulk_item_promo_with_discount(customer_fidelity_0) -> None:
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cart = [LineItem('banana', 30, .5),
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LineItem('apple', 10, 1.5)]
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order = Order(customer_fidelity_0, 10, BulkItemPromo())
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assert order.total() == 30.0
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assert order.due() == 28.5
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Now Mypy complains that "Argument 2 of Order has incompatible type".
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However, even with the annotation in the test function signature,
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Mypy did not find any problem when I mistyped the name of the ``cart`` argument.
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Here, ``cart_plain`` should be ``cart``::
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def test_bulk_item_promo_with_discount(customer_fidelity_0) -> None:
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cart = [LineItem('banana', 30, .5),
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LineItem('apple', 10, 1.5)]
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order = Order(customer_fidelity_0, cart_plain, BulkItemPromo())
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assert order.total() == 30.0
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assert order.due() == 28.5
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Hypotesis: ``cart_plain`` is a function decorated with ``@pytest.fixture``,
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and at the top of the test file I told Mypy to ignore the Pytest import::
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import pytest # type: ignore
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