From da90fb559ebd16ac293f9bfdc1ab2dc8882ef4e0 Mon Sep 17 00:00:00 2001 From: geekpi Date: Tue, 21 May 2019 08:51:40 +0800 Subject: [PATCH] translated --- ...oactively in Python with singledispatch.md | 106 ------------------ ...oactively in Python with singledispatch.md | 106 ++++++++++++++++++ 2 files changed, 106 insertions(+), 106 deletions(-) delete mode 100644 sources/tech/20190504 Add methods retroactively in Python with singledispatch.md create mode 100644 translated/tech/20190504 Add methods retroactively in Python with singledispatch.md diff --git a/sources/tech/20190504 Add methods retroactively in Python with singledispatch.md b/sources/tech/20190504 Add methods retroactively in Python with singledispatch.md deleted file mode 100644 index 92f5063d57..0000000000 --- a/sources/tech/20190504 Add methods retroactively in Python with singledispatch.md +++ /dev/null @@ -1,106 +0,0 @@ -[#]: collector: (lujun9972) -[#]: translator: (geekpi) -[#]: reviewer: ( ) -[#]: publisher: ( ) -[#]: url: ( ) -[#]: subject: (Add methods retroactively in Python with singledispatch) -[#]: via: (https://opensource.com/article/19/5/python-singledispatch) -[#]: author: (Moshe Zadka https://opensource.com/users/moshez) - -Add methods retroactively in Python with singledispatch -====== -Learn more about solving common Python problems in our series covering -seven PyPI libraries. -![][1] - -Python is one of the most [popular programming languages][2] in use today—and for good reasons: it's open source, it has a wide range of uses (such as web programming, business applications, games, scientific programming, and much more), and it has a vibrant and dedicated community supporting it. This community is the reason we have such a large, diverse range of software packages available in the [Python Package Index][3] (PyPI) to extend and improve Python and solve the inevitable glitches that crop up. - -In this series, we'll look at seven PyPI libraries that can help you solve common Python problems. Today, we'll examine [**singledispatch**][4], a library that allows you to add methods to Python libraries retroactively. - -### singledispatch - -Imagine you have a "shapes" library with a **Circle** class, a **Square** class, etc. - -A **Circle** has a **radius** , a **Square** has a **side** , and a **Rectangle** has **height** and **width**. Our library already exists; we do not want to change it. - -However, we do want to add an **area** calculation to our library. If we didn't share this library with anyone else, we could just add an **area** method so we could call **shape.area()** and not worry about what the shape is. - -While it is possible to reach into a class and add a method, this is a bad idea: nobody expects their class to grow new methods, and things might break in weird ways. - -Instead, the **singledispatch** function in **functools** can come to our rescue. - - -``` -@singledispatch -def get_area(shape): -raise NotImplementedError("cannot calculate area for unknown shape", -shape) -``` - -The "base" implementation for the **get_area** function fails. This makes sure that if we get a new shape, we will fail cleanly instead of returning a nonsense result. - - -``` -@get_area.register(Square) -def _get_area_square(shape): -return shape.side ** 2 -@get_area.register(Circle) -def _get_area_circle(shape): -return math.pi * (shape.radius ** 2) -``` - -One nice thing about doing things this way is that if someone writes a _new_ shape that is intended to play well with our code, they can implement **get_area** themselves. - - -``` -from area_calculator import get_area - -@attr.s(auto_attribs=True, frozen=True) -class Ellipse: -horizontal_axis: float -vertical_axis: float - -@get_area.register(Ellipse) -def _get_area_ellipse(shape): -return math.pi * shape.horizontal_axis * shape.vertical_axis -``` - -_Calling_ **get_area** is straightforward. - - -``` -`print(get_area(shape))` -``` - -This means we can change a function that has a long **if isintance()/elif isinstance()** chain to work this way, without changing the interface. The next time you are tempted to check **if isinstance** , try using **singledispatch**! - -In the next article in this series, we'll look at **tox** , a tool for automating tests on Python code. - -#### Review the previous articles in this series: - - * [Cython][5] - * [Black][6] - * [attrs][7] - - - --------------------------------------------------------------------------------- - -via: https://opensource.com/article/19/5/python-singledispatch - -作者：[Moshe Zadka ][a] -选题：[lujun9972][b] -译者：[译者ID](https://github.com/译者ID) -校对：[校对者ID](https://github.com/校对者ID) - -本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 - -[a]: https://opensource.com/users/moshez -[b]: https://github.com/lujun9972 -[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/computer_code_programming_laptop.jpg?itok=ormv35tV -[2]: https://opensource.com/article/18/5/numbers-python-community-trends -[3]: https://pypi.org/ -[4]: https://pypi.org/project/singledispatch/ -[5]: https://opensource.com/article/19/4/7-python-problems-solved-cython -[6]: https://opensource.com/article/19/4/python-problems-solved-black -[7]: https://opensource.com/article/19/4/python-problems-solved-attrs diff --git a/translated/tech/20190504 Add methods retroactively in Python with singledispatch.md b/translated/tech/20190504 Add methods retroactively in Python with singledispatch.md new file mode 100644 index 0000000000..40fae67d1a --- /dev/null +++ b/translated/tech/20190504 Add methods retroactively in Python with singledispatch.md @@ -0,0 +1,106 @@ +[#]: collector: (lujun9972) +[#]: translator: (geekpi) +[#]: reviewer: ( ) +[#]: publisher: ( ) +[#]: url: ( ) +[#]: subject: (Add methods retroactively in Python with singledispatch) +[#]: via: (https://opensource.com/article/19/5/python-singledispatch) +[#]: author: (Moshe Zadka https://opensource.com/users/moshez) + +使用 singledispatch 在 Python 中追溯地添加方法 +====== +在我们覆盖 7 个 PyPI 库的系列文章中了解更多解决 Python 问题的信息。 +![][1] + +Python 是当今使用最多[流行的编程语言][2]之一，因为：它是开源的，它具有广泛的用途（例如 Web 编程、业务应用、游戏、科学编程等等），它有一个充满活力和专注的社区支持它。这个社区是我们在 [Python Package Index][3]（PyPI）中提供如此庞大、多样化的软件包的原因，用以扩展和改进 Python。并解决不可避免的问题。 + +在本系列中，我们将介绍七个可以帮助你解决常见 Python 问题的 PyPI 库。今天，我们将研究 [**singledispatch**][4]，这是一个能让你追溯地向 Python 库添加方法的库。 + +### singledispatch + +想象一下，你有一个有 **Circle**、**Square** 等类的“形状”库。 + +**Circle** 类有**半径**、**Square** 有 **边**、**Rectangle**有**高**和**宽**。我们的库已经存在，我们不想改变它。 + +然而，我们想给库添加一个**面积**计算。如果我们不会和其他人共享这个库，我们只需添加 **area** 方法，这样我们就能调用 **shape.area()** 而无需关心是什么形状。 + +虽然可以进入类并添加一个方法，但这是一个坏主意：没有人希望他们的类会被添加新的方法，程序因奇怪的方式出错。 + +相反，**functools** 中的 **singledispatch** 函数可以帮助我们。 + + +``` +@singledispatch +def get_area(shape): + raise NotImplementedError("cannot calculate area for unknown shape", + shape) +``` + +**get_area** 函数的“基类”实现会报错。这保证了如果我们出现一个新的形状时，我们会明确地报错而不是返回一个无意义的结果。 + + +``` +@get_area.register(Square) +def _get_area_square(shape): + return shape.side ** 2 +@get_area.register(Circle) +def _get_area_circle(shape): + return math.pi * (shape.radius ** 2) +``` + +这种方式的好处是如果某人写了一个匹配我们代码的_新_形状，它们可以自己实现 **get_area**。 + + +``` +from area_calculator import get_area + +@attr.s(auto_attribs=True, frozen=True) +class Ellipse: + horizontal_axis: float + vertical_axis: float + +@get_area.register(Ellipse) +def _get_area_ellipse(shape): + return math.pi * shape.horizontal_axis * shape.vertical_axis +``` + +_调用_ **get_area** 很直接。 + + +``` +`print(get_area(shape))` +``` + +这意味着我们可以将有大量 **if isintance()/elif isinstance()** 的代码以这种方式修改，而无需修改接口。下一次你要修改 **if isinstance**，你试试 **singledispatch**！ + +在本系列的下一篇文章中，我们将介绍 **tox**，一个用于自动化 Python 代码测试的工具。 + + +#### 回顾本系列的前几篇文章： + + * [Cython][5] + * [Black][6] + * [attrs][7] + + + +-------------------------------------------------------------------------------- + +via: https://opensource.com/article/19/5/python-singledispatch + +作者：[Moshe Zadka ][a] +选题：[lujun9972][b] +译者：[geekpi](https://github.com/geekpi) +校对：[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 + +[a]: https://opensource.com/users/moshez +[b]: https://github.com/lujun9972 +[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/computer_code_programming_laptop.jpg?itok=ormv35tV +[2]: https://opensource.com/article/18/5/numbers-python-community-trends +[3]: https://pypi.org/ +[4]: https://pypi.org/project/singledispatch/ +[5]: https://opensource.com/article/19/4/7-python-problems-solved-cython +[6]: https://opensource.com/article/19/4/python-problems-solved-black +[7]: https://opensource.com/article/19/4/python-problems-solved-attrs