How to start using types in Python with mypy

How to start using types in Python with mypy

• 1.
  How to startusing types in Python with Mypy
• 2.
  Carlos Villavicencio Ecuadorian 󰎸 Software Developerat Stack Builders Community leader Amateur photographer cvillavicencio cvillavicencio@stackbuilders.com @po5i po5i Quilotoa Lake, Ecuador 2020. 大家好!
• 3.
  Types and Python
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  Data Structures Primitive Non-primitive IntegerFloat String Boolean Array List Tuple Dictionary Set File Linear Non-linear Stacks Queues Graphs Trees
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  Types are knownin compilation time Variables bind to types Very verbose Bytecode is well optimized in memory Types are known in runtime Variables bind to objects 🦆 Less verbose Bugs in run-time are very common Dynamic vs. Static Languages
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  Weakly vs. StronglyType System Implicit coercion between non-related types Flexibles Unpredictables Explicit type conversion (casting) Strict rules on the static analysis. Type Safety
• 9.
  Static type checking inPython But you can also use
• 10.
  Type Annotations
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  meat: str ="Beef" weight_pounds: float = "0.5" # mypy # error: Incompatible types in assignment # (expression has type "str", variable has type "float") Primitive types 🦕
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  Let’s prepare some🍔 def make_hamburger(meat, number_of_meats): return ["bread"] + [meat] * number_of_meats + ["bread"] print(make_hamburger("BEEF", 2)) # ['bread', 'BEEF', 'BEEF', 'bread']
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  class MyTest(unittest.TestCase): def test_make_hamburger_returns_list(self): self.assertTrue(isinstance(make_hamburger("beef",2), list)) def test_empty_make_hamburger_returns_breads(self): self.assertEqual(make_hamburger(None, 0), ['bread', 'bread']) def test_invalid_make_hamburger_raises(self): with self.assertRaises(TypeError): make_hamburger() Unit testing?
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  from typing importList def make_hamburger(meat: str, number_of_meats: int) -> List[str]: return ["bread"] + [meat] * number_of_meats + ["bread"] The `typing`module
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  from typing importList Hamburger = List[str] def make_hamburger(meat: str, number_of_meats: int) -> Hamburger: return ["bread"] + [meat] * number_of_meats + ["bread"] Type Alias
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  from typing importList, Optional Hamburger = List[str] Extras = Optional[List[str]] def make_hamburger(meat: str, number_of_meats: int, extras: Extras) -> Hamburger: if extras: return ["bread"] + extras + [meat] * number_of_meats + ["bread"] else: return ["bread"] + [meat] * number_of_meats + ["bread"] print(make_hamburger("Beef", 2, ['tomatoes', 'pickles'])) # ['bread', 'tomatoes', 'pickles', 'Beef', 'Beef', 'bread'] Optionals 🍅
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  from typing importTypeVar, List T = TypeVar("T", int, List[str]) def generic_add(x: T, y: T) -> T: return x + y Generics 󰟲
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  x1: int =5 y1: int = 2 print(generic_add(x1, y1)) # 7 x2: List[str] = ["Hello"] y2: List[str] = ["World"] print(generic_add(x2, y2)) # ['Hello', 'World'] x3: str = "foo" y3: str = "bar" print(generic_add(x3, y3)) # mypy error: Value of type variable "T" of "generic_add" cannot be "str" Generics 󰟲
• 19.
  from typing importUnion Number = Union[float, int] def union_add(x: Number, y: Number) -> Number: return x + y Union Types
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  x1: int =5 y1: float = 2.5 print(union_add(x1, y1)) # 7 x2: int = 2 y2: str = "1" print(union_add(x2, y2)) # error: Argument 1 to "union_add" has incompatible type "str"; expected "Union[float, int]" # error: Argument 2 to "union_add" has incompatible type "str"; expected "Union[float, int]" Union Types
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  from typing importCallable def sum_and_process(a: int, b: int, callback: Callable[[int], bool]) -> bool: total = a + b return callback(total) def is_positive(val: int) -> bool: return val > 0 output = sum_and_process(5, 2, is_positive) print(output) # True Callables
• 23.
  谢谢! ευχαριστώ Obrigado! ¡Gracias! Thank You! Check outmy tutorial