选题[tech]: 20210520 Make your API better with this positional trick from Python 3.8

sources/tech/20210520 Make your API better with this positional trick from Python 3.8.md

sources/tech/20210520 Make your API better with this positional trick from Python 3.8.md

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+[#]: subject: (Make your API better with this positional trick from Python 3.8)
+[#]: via: (https://opensource.com/article/21/5/python-38-features)
+[#]: author: (Moshe Zadka https://opensource.com/users/moshez)
+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+
+Make your API better with this positional trick from Python 3.8
+======
+Explore positional-only parameters and two other underutilized but still
+useful Python features.
+![Women in computing and open source v5][1]
+
+This is the ninth in a series of articles about features that first appeared in a version of Python 3.x. Python 3.8 was first released in 2019, and two years later, many of its cool new features remain underused. Here are three of them.
+
+### importlib.metadata
+
+[Entry points][2] are used for various things in Python packages. The most familiar are [console_scripts][3] entrypoints, but many plugin systems in Python use them.
+
+Until Python 3.8, the best way to read entry points from Python was to use `pkg_resources`, a somewhat clunky module that is part of `setuptools`.
+
+The new `importlib.metadata` is a built-in module that allows access to the same thing:
+
+
+```
+from importlib import metadata as importlib_metadata
+
+distribution = importlib_metadata.distribution("numpy")
+distribution.entry_points
+
+[/code] [code]
+
+    [EntryPoint(name='f2py', value='numpy.f2py.f2py2e:main', group='console_scripts'),
+     EntryPoint(name='f2py3', value='numpy.f2py.f2py2e:main', group='console_scripts'),
+     EntryPoint(name='f2py3.9', value='numpy.f2py.f2py2e:main', group='console_scripts')]
+```
+
+Entry points are not the only thing `importlib.metadata` permits access to. For debugging, reporting, or (in extreme circumstances) triggering compatibility modes, you can also check the version of dependencies—at runtime!
+
+
+```
+`f"{distribution.metadata['name']}=={distribution.version}"`[/code] [code]`    'numpy==1.20.1'`
+```
+
+### Positional-only parameters
+
+After the wild success of keywords-only arguments at communicating API authors' intentions, another gap was filled: positional-only arguments.
+
+Especially for functions that allow arbitrary keywords (for example, to generate data structures), this means there are fewer constraints on allowed argument names:
+
+
+```
+def some_func(prefix, /, **kwargs):
+    print(prefix, kwargs)
+
+[/code] [code]`some_func("a_prefix", prefix="prefix keyword value")`[/code] [code]`    a_prefix {'prefix': 'prefix keyword value'}`
+```
+
+Note that, confusingly, the value of the _variable_ `prefix` is distinct from the value of `kwargs["prefix"]`. As in many places, take care to use this feature carefully.
+
+### Self-debugging expressions
+
+The `print()` statement (and its equivalent in other languages) has been a favorite for quickly debugging output for over 50 years.
+
+But we have made much progress in print statements like:
+
+
+```
+special_number = 5
+print("special_number = %s" % special_number)
+
+[/code] [code]`    special_number = 5`
+```
+
+Yet self-documenting f-strings make it even easier to be clear:
+
+
+```
+`print(f"{special_number=}")`[/code] [code]`    special_number=5`
+```
+
+Adding an `=` to the end of an f-string interpolated section keeps the literal part while adding the value.
+
+This is even more useful when more complicated expressions are inside the section:
+
+
+```
+values = {}
+print(f"{values.get('something', 'default')=}")
+
+[/code] [code]`    values.get('something', 'default')='default'`
+```
+
+### Welcome to 2019
+
+Python 3.8 was released about two years ago, and some of its new features are cool—and underused. Add them to your toolkit if you haven't already.
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/21/5/python-38-features
+
+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/OSDC_women_computing_5.png?itok=YHpNs_ss (Women in computing and open source v5)
+[2]: https://packaging.python.org/specifications/entry-points/
+[3]: https://python-packaging.readthedocs.io/en/latest/command-line-scripts.html