PythonAdvanced

Type Hints

Python type hints and annotations: annotate function parameters, return types, variables, and use Optional and typing generics.

01Annotate a function

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main.py

def greet(name: str) -> str:
    return "Hello, " + name

print(greet("World"))

Output

Hello, World

02Variable annotations

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main.py

age: int = 25
height: float = 1.75
name: str = "Ada"
print(age, height, name)

Output

25 1.75 Ada

03Typed list parameter

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main.py

from typing import List
def total(nums: List[int]) -> int:
    return sum(nums)

print(total([1, 2, 3, 4]))

Output

04Optional return value

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main.py

from typing import Optional
def find(x: int) -> Optional[str]:
    if x > 0:
        return "positive"
    return None

print(find(5))
print(find(-1))

Output

positive
None