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geekpi
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[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Say goodbye to boilerplate in Python with attrs)
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[#]: via: (https://opensource.com/article/19/5/python-attrs)
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[#]: author: (Moshe Zadka https://opensource.com/users/moshez/users/moshez)
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Say goodbye to boilerplate in Python with attrs
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======
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Learn more about solving common Python problems in our series covering
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seven PyPI libraries.
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![Programming at a browser, orange hands][1]
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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.
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In this series, we'll look at seven PyPI libraries that can help you solve common Python problems. Today, we'll examine [**attrs**][4], a Python package that helps you write concise, correct code quickly.
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### attrs
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If you have been using Python for any length of time, you are probably used to writing code like:
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```
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class Book(object):
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def __init__(self, isbn, name, author):
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self.isbn = isbn
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self.name = name
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self.author = author
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```
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Then you write a **__repr__** function; otherwise, it would be hard to log instances of **Book** :
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```
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def __repr__(self):
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return f"Book({self.isbn}, {self.name}, {self.author})"
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```
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Next, you write a nice docstring documenting the expected types. But you notice you forgot to add the **edition** and **published_year** attributes, so you have to modify them in five places.
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What if you didn't have to?
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```
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@attr.s(auto_attribs=True)
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class Book(object):
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isbn: str
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name: str
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author: str
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published_year: int
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edition: int
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```
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Annotating the attributes with types using the new type annotation syntax, **attrs** detects the annotations and creates a class.
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ISBNs have a specific format. What if we want to enforce that format?
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```
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@attr.s(auto_attribs=True)
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class Book(object):
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isbn: str = attr.ib()
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@isbn.validator
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def pattern_match(self, attribute, value):
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m = re.match(r"^(\d{3}-)\d{1,3}-\d{2,3}-\d{1,7}-\d$", value)
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if not m:
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raise ValueError("incorrect format for isbn", value)
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name: str
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author: str
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published_year: int
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edition: int
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```
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The **attrs** library also has great support for [immutability-style programming][5]. Changing the first line to **@attr.s(auto_attribs=True, frozen=True)** means that **Book** is now immutable: trying to modify an attribute will raise an exception. Instead, we can get a _new_ instance with modification using **attr.evolve(old_book, published_year=old_book.published_year+1)** , for example, if we need to push publication forward by a year.
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In the next article in this series, we'll look at **singledispatch** , a library that allows you to add methods to Python libraries retroactively.
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#### Review the previous articles in this series
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* [Cython][6]
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* [Black][7]
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/19/5/python-attrs
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作者：[Moshe Zadka ][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/moshez/users/moshez
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/programming_code_keyboard_orange_hands.png?itok=G6tJ_64Y (Programming at a browser, orange hands)
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[2]: https://opensource.com/article/18/5/numbers-python-community-trends
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[3]: https://pypi.org/
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[4]: https://pypi.org/project/attrs/
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[5]: https://opensource.com/article/18/10/functional-programming-python-immutable-data-structures
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[6]: https://opensource.com/article/19/4/7-python-problems-solved-cython
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[7]: https://opensource.com/article/19/4/python-problems-solved-black
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@ -0,0 +1,106 @@
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[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Say goodbye to boilerplate in Python with attrs)
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[#]: via: (https://opensource.com/article/19/5/python-attrs)
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[#]: author: (Moshe Zadka https://opensource.com/users/moshez/users/moshez)
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使用 attrs 来告别 Python 中的样板
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======
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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。
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![Programming at a browser, orange hands][1]
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Python是当今使用最多[流行的编程语言] [2]之一 - 并且有充分的理由：它是开源的，它具有广泛的用途（例如Web编程，业务应用程序，游戏，科学编程等等）更多），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，以扩展和改进Python并解决不可避免的问题。
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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 [**attrs**][4]，这是一个帮助你快速编写简洁，正确的代码的 Python 包。
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### attrs
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如果你已经写过一段时间的 Python，那么你可能习惯这样写代码：
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```
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class Book(object):
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def __init__(self, isbn, name, author):
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self.isbn = isbn
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self.name = name
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self.author = author
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```
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接着写一个 **__repr__** 函数。否则，很难记录 **Book** 的实例：
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```
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def __repr__(self):
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return f"Book({self.isbn}, {self.name}, {self.author})"
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```
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接下来你会写一个好看的 docstring 来记录期望的类型。但是你注意到你忘了添加 **edition** 和 **published_year** 属性，所以你必须在五个地方修改它们。
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如果你不必这么做如何？
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```
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@attr.s(auto_attribs=True)
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class Book(object):
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isbn: str
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name: str
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author: str
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published_year: int
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edition: int
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```
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使用新的类型注释语法注释类型属性，**attrs** 会检测注释并创建一个类。
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ISBN 有特定格式。如果我们想强行使用该格式怎么办？
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```
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@attr.s(auto_attribs=True)
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class Book(object):
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isbn: str = attr.ib()
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@isbn.validator
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def pattern_match(self, attribute, value):
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m = re.match(r"^(\d{3}-)\d{1,3}-\d{2,3}-\d{1,7}-\d$", value)
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if not m:
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raise ValueError("incorrect format for isbn", value)
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name: str
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author: str
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published_year: int
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edition: int
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```
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**attrs** 库也对[不可变风格编程][5]支持良好。将第一行改成 **@attr.s(auto_attribs=True, frozen=True)** 意味着 **Book** 现在是不可变的：尝试修改一个属性将会引发一个异常。相反，比如，如果希望将发布日期向后一年，我们可以修改成 **attr.evolve(old_book, published_year=old_book.published_year+1)** 来得到一个_新的_实例。
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本系列的下一篇文章我们将来看下 **singledispatch**，一个能让你向 Python 库添加方法的库。
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#### 查看本系列先前的文章
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* [Cython][6]
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* [Black][7]
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/19/5/python-attrs
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作者：[Moshe Zadka ][a]
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选题：[lujun9972][b]
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译者：[geekpi](https://github.com/geekpi)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/moshez/users/moshez
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/programming_code_keyboard_orange_hands.png?itok=G6tJ_64Y (Programming at a browser, orange hands)
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[2]: https://opensource.com/article/18/5/numbers-python-community-trends
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[3]: https://pypi.org/
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[4]: https://pypi.org/project/attrs/
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[5]: https://opensource.com/article/18/10/functional-programming-python-immutable-data-structures
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[6]: https://opensource.com/article/19/4/7-python-problems-solved-cython
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[7]: https://opensource.com/article/19/4/python-problems-solved-black
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