Merge pull request #13534 from lujun9972/add-MjAxOTA1MDMgU2F5IGdvb2RieWUgdG8gYm9pbGVycGxhdGUgaW4gUHl0aG9uIHdpdGggYXR0cnMubWQK

选题: 20190503 Say goodbye to boilerplate in Python with attrs

sources/tech/20190503 Say goodbye to boilerplate in Python with attrs.md

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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (Say goodbye to boilerplate in Python with attrs)
+[#]: via: (https://opensource.com/article/19/5/python-attrs)
+[#]: author: (Moshe Zadka  https://opensource.com/users/moshez/users/moshez)
+
+Say goodbye to boilerplate in Python with attrs
+======
+Learn more about solving common Python problems in our series covering
+seven PyPI libraries.
+![Programming at a browser, orange hands][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 [**attrs**][4], a Python package that helps you write concise, correct code quickly.
+
+### attrs
+
+If you have been using Python for any length of time, you are probably used to writing code like:
+
+
+```
+class Book(object):
+
+def __init__(self, isbn, name, author):
+self.isbn = isbn
+self.name = name
+self.author = author
+```
+
+Then you write a **__repr__** function; otherwise, it would be hard to log instances of **Book** :
+
+
+```
+def __repr__(self):
+return f"Book({self.isbn}, {self.name}, {self.author})"
+```
+
+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.
+
+What if you didn't have to?
+
+
+```
+@attr.s(auto_attribs=True)
+class Book(object):
+isbn: str
+name: str
+author: str
+published_year: int
+edition: int
+```
+
+Annotating the attributes with types using the new type annotation syntax, **attrs** detects the annotations and creates a class.
+
+ISBNs have a specific format. What if we want to enforce that format?
+
+
+```
+@attr.s(auto_attribs=True)
+class Book(object):
+isbn: str = attr.ib()
+@isbn.validator
+def pattern_match(self, attribute, value):
+m = re.match(r"^(\d{3}-)\d{1,3}-\d{2,3}-\d{1,7}-\d$", value)
+if not m:
+raise ValueError("incorrect format for isbn", value)
+name: str
+author: str
+published_year: int
+edition: int
+```
+
+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.
+
+In the next article in this series, we'll look at **singledispatch** , a library that allows you to add methods to Python libraries retroactively.
+
+#### Review the previous articles in this series
+
+  * [Cython][6]
+  * [Black][7]
+
+
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/19/5/python-attrs
+
+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/users/moshez
+[b]: https://github.com/lujun9972
+[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)
+[2]: https://opensource.com/article/18/5/numbers-python-community-trends
+[3]: https://pypi.org/
+[4]: https://pypi.org/project/attrs/
+[5]: https://opensource.com/article/18/10/functional-programming-python-immutable-data-structures
+[6]: https://opensource.com/article/19/4/7-python-problems-solved-cython
+[7]: https://opensource.com/article/19/4/python-problems-solved-black