This is an overview about static typing including a small tutorial. * What is is * Why * How does it look like? ca. 30 mins

1. Static Type Checking in Python
Sebastian Wagner, swagner@suse.com
Ceph component lead
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2. Where is the Problem?Where is the Problem?
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3. In a nutshell
Static typing vs. dynamic typing
Type annotations
mypy - http://mypy-lang.org/
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4. Would I bene t from static typing?
Project is large or complex.
code base must be maintained for a long time.
Multiple developers are working on the same code
You're learning Python.
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5. Where can static typing help?
Correct arguments to functions and operators
Spelling mistakes
Type compatibility check
None - a loophole in the type system
API Documentation
Editor support
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6. Editor support
Error Highlighting:
Parameter Documentation
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7. Editor support (2)
Code Completion:
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8. Of course, it has limitations.Of course, it has limitations.
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9. Syntax
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10. Syntax: Functions
def stringify(num: int) -> str:
return str(num)
def add(num1: int, my_float: float = 3.5) -> float:
return num1 + my_float
add(1, 'string')
Running mypy reveals:
error: Argument 2 to "add" has incompatible type "str"; expected "float"
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11. Syntax: Variables
my_var: int = 1
my_var: float = 1.0
my_var: bool = True
my_var: str = "test"
my_var: bytes = b"test"
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12. Syntax: Using Generics
from typing import List, Set, Dict, Tuple
my_var: List[int] = [1]
my_var: Tuple[int, str] = (1, 'hello')
my_var: Set[int] = {6, 7}
my_var: Dict[int, str] = {6: 'six', 7: 'seven'}
from typing import List, Union, Optional
my_var: List[Union[int, str]] = [3, 5, "test", "fun"]
my_var: Optional[str] = None
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13. Syntax: Classes
from typing import List
class MyClass:
charge_percent: int = 100
def __init__(self, items: List[str]) -> None:
self.items = items
def my_method(self, num: int, str1: str) -> str:
return num * str1
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14. Syntax: Escape routes
from typing import Any
my_var: Any = mystery_function()
my_var = confusing_function() # type: ignore
Don't confuse with object!
Forward References
def f(foo: 'A') -> int
...
class A:
...
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15. Syntax: Python 2
def add(num1, my_float = 3.5):
# type: (int, float) -> float
return num1 + my_float
my_var = 'hello' # type: str
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16. Stub les
Interface file for type hints only
.pyi
Cython bindings
Native code
typeshed
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17. Legacy Code
Generate type annotations
pyannotate
MonkeyType
Focus on modules that are imported often.
Write a script that runs mypy on the whole code base
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18. Questions?Questions?
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19. Thank youThank you
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