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85 lines
3.4 KiB
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[#]: subject: (3 features released in Python 3.1 you should use in 2021)
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[#]: via: (https://opensource.com/article/21/5/python-31-features)
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[#]: author: (Moshe Zadka https://opensource.com/users/moshez)
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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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你应该在 2021 年使用的 Python 3.1 中发布的 3 个功能
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======
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探索一些未被充分利用但仍然有用的 Python 特性。
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![Python programming language logo with question marks][1]
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这是关于首次出现在 Python 3.x 版本中的特性的系列文章的第二篇。Python 3.1 于 2009 年首次发布，尽管它已经发布了很长时间，但它引入的许多特性都没有被充分利用，而且相当酷。下面是其中的三个。
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### 千位数格式化
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在格式化大数时，通常是每三位数放置逗号，使数字更易读 (例如，1,048,576 比 1048576 更容易读)。从 Python 3.1 开始，可以在使用字符串格式化函数时直接完成：
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```
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`"2 to the 20th power is {:,d}".format(2**20)`[/code] [code]`'2 to the 20th power is 1,048,576'`
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```
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`,d` 格式符表示数字必须用逗号格式化。
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### Counter 类
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`collections.Counter` 类是标准库模块 `collections` 的一部分，是 Python 中的一个秘密超级武器。它经常在 Python 的面试题的简单解答中首次遇到，但它的价值并不限于此。
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例如，在 [Humpty Dumpty 的歌][2]的前八行中找出五个最常见的字母：
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```
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hd_song = """
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In winter, when the fields are white,
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I sing this song for your delight.
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In Spring, when woods are getting green,
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I'll try and tell you what I mean.
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In Summer, when the days are long,
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Perhaps you'll understand the song.
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In Autumn, when the leaves are brown,
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Take pen and ink, and write it down.
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"""
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```
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```
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import collections
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collections.Counter(hd_song.lower().replace(' ', '')).most_common(5)
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```
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```
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`[('e', 29), ('n', 27), ('i', 18), ('t', 18), ('r', 15)]`
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```
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### 执行软件包
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Python 允许使用 `-m` 标志来从命令行执行模块。甚至一些标准库模块在被执行时也会做一些有用的事情；例如，`python -m cgi` 是一个 CGI 脚本，用来调试网络服务器的 CGI 配置。
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然而，直到 Python 3.1，都不可能像这样执行_软件包_。从 Python 3.1 开始，`python -m package` 将执行软件包中的 `__main__` 模块。这是一个放调试脚本或命令的好地方，这些脚本主要是用工具执行的，不需要很短。
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Python 3.0 在 11 年前就已经发布了，但是在这个版本中首次出现的一些功能是很酷的，而且没有得到充分利用。如果你还没使用，那么将它们添加到你的工具箱中。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/5/python-31-features
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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
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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/python_programming_question.png?itok=cOeJW-8r (Python programming language logo with question marks)
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[2]: http://www2.open.ac.uk/openlearn/poetryprescription/humpty-dumptys-recitation.html
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