Overtake

How to install?

pip install overtake

What is Overtake?

Overtake is a small library made to push @typing.overload even further. @typing.overload just defines signatures, so that type checkers know what type hints are available when calling a function. With Overtake, you can also call those functions at runtime, similar to languages like C++ or Julia.

An example is worth a thousand words:

from typing import overload

# if you are using Python <3.11, you'll need instead
# from typing_extensions import overload

from overtake import overtake


@overload
def count_words(input_value: str) -> int:
    return len(input_value.split(" "))


@overload
def count_words(input_value: list[str]) -> int:
    total = 0
    for text in input_value:
        total += len(text.split(" "))
    return total


@overtake
def count_words(input_value):
    ...


print(count_words("Python is fun!"))
# 3
print(count_words(["hello world", "other piece of text"]))
# 6

Overtake will analyse the types and provided arguments to call the right implementation.

It works for every type hint supported by the awesome beartype. It works for every signature supported by @typing.overload

This pattern is supported by IDEs (Pycharm, VSCode, etc...) so autocompletion will work well. It's also supported as well by type checkers (Mypy, Pyright, etc...) so you don't need to compromise on type safety 😁

Overtake follow closely the Mypy guide on @typing.overload: https://mypy.readthedocs.io/en/stable/more_types.html#function-overloading

More advanced examples.

We can show you here more pattern that are possible. Basically if isinstance(..., ...) might be your cue that overtake might help you write clearer code.

Recursivity

Let's write a function that returns the number of days since January 1st:

from typing import overload
from datetime import date

from overtake import overtake


@overload
def days_this_year(current_date: date) -> int:
    delta = current_date - date(2023, 1, 1)
    return delta.days


@overload
def days_this_year(current_date: str) -> int:
    return days_this_year(date.fromisoformat(current_date))


@overtake
def days_this_year(current_date):
    ...


print(days_this_year(date(2023, 8, 15)))
# 226
print(days_this_year("2023-08-15"))
# 226

You can call your function in a recursive manner, to deduplicate code. We could actually rewrite our first example like this:

from typing import overload

from overtake import overtake


@overload
def count_words(input_value: str) -> int:
    return len(input_value.split(" "))


@overload
def count_words(input_value: list[str]) -> int:
    total = 0
    for text in input_value:
        total += count_words(text)
    return total


@overtake
def count_words(input_value):
    ...


print(count_words("Python is fun!"))
# 3
print(count_words(["hello world", "other piece of text"]))
# 6

Different output types

It's also possible to have different output types, like with @overload

from typing import overload

from overtake import overtake


@overload
def convert_to_int(input_value: str) -> int:
    return int(input_value)


@overload
def convert_to_int(input_value: list[str]) -> list[int]:
    return [int(x) for x in input_value]


@overtake
def convert_to_int(input_value):
    ...


print(convert_to_int("88"))
# 88 (an integer)
print(convert_to_int(["88", "42", "84"]))
# [88, 42, 84] (a list of integers)

Leveraging optional arguments

It can avoid some annoying uses of if ... is None:, you can specify different number of arguments (but the order must match!).

For this example, let's say that you want the user to be able to write some text in any kind of file. If the file is not provided, we create a temporary file. We must accept any input for the file. A str, a pathlib.Path, a file-like object too. Or nothing (random file).

from typing import overload
from pathlib import Path
import io
import random

from overtake import overtake


@overload
def write_text_to_file(text: str, file: io.TextIOBase) -> None:
    file.write(text)


@overload
def write_text_to_file(text: str, file: Path) -> Path:
    file.write_text(text)
    return file


@overload
def write_text_to_file(text: str, file: str) -> Path:
    return write_text_to_file(text, Path(file))


@overload
def write_text_to_file(text: str) -> Path:
    random_file_name = f"/tmp/{random.randint(0, 10)}.txt"
    return write_text_to_file(text, random_file_name)


@overtake
def write_text_to_file(text, file=None):
    ...


print(write_text_to_file("hello world"))
# /tmp/4.txt
print(write_text_to_file("hello world", "/tmp/some-file.txt"))
# /tmp/some-file.txt
print(write_text_to_file("hello world", Path("/tmp/some-file.txt")))
# /tmp/some-file.txt
print(write_text_to_file("hello world", io.StringIO()))
# None (we didn't write in a file on disk)

Recommendations

We recommend using a type checker of your choice (Mypy, Pyright, etc...) so that the type checker catches invalid usages of @overload. Even though it's not mandatory, it's helpful to catch mistakes with @overload early.

Compatibility with Pyright

Pyright has a small compatibility issue, you might get the following error:

error: "my_function" is marked as overload, but it includes an implementation
The body of a function overload should be "..."

This can be fixed without disabling type checking on calls and function bodies by adding # type: ignore next to the overloaded function signatures. Here is a small example:

from datetime import date

from overtake import overtake
from typing_extensions import overload


@overload
def days_this_year(current_date: date) -> int:  # type: ignore
    delta = current_date - date(2023, 1, 1)
    return delta.days


@overload
def days_this_year(current_date: str) -> int:  # type: ignore
    return days_this_year(date.fromisoformat(current_date))


@overtake
def days_this_year(current_date):
    ...