help() 输出中的斜杠是什么意思? [英] What does the slash mean in help() output?
问题描述
/
在 Python 3.4 的 help
输出中,range
在右括号前是什么意思?
它标志着仅定位参数,您不能用作关键字参数的参数.在 Python 3.8 之前,此类参数只能在 C API 中指定.
这意味着 __contains__
的 key
参数只能按位置传入 (range(5).__contains__(3)
),不是作为关键字参数 (range(5).__contains__(key=3)
),你可以在纯 python 函数中用位置参数做的事情.
另请参阅 Argument Clinic 文档:
<块引用>要在 Argument Clinic 中将所有参数标记为仅位置参数,请在最后一个参数后的一行中单独添加一个 /
,缩进与参数行相同.
和(最近添加的)Python 常见问题:
<块引用>函数参数列表中的斜线表示它之前的参数是仅位置参数.仅位置参数是没有外部可用名称的参数.在调用仅接受位置参数的函数时,参数将仅根据其位置映射到参数.
语法现在是 Python 语言规范的一部分,作为3.8 版,参见 PEP 570 – Python Positional-Only 参数.在 PEP 570 之前,该语法已经保留以供将来可能包含在 Python 中,请参阅 PEP 457 -仅位置参数的语法.
仅位置参数可以带来更清晰和更清晰的 API,使其他仅使用 C 的模块的纯 Python 实现更加一致且更易于维护,并且由于仅位置参数需要很少的处理,因此它们可以生成更快的 Python 代码.
What does the /
mean in Python 3.4's help
output for range
before the closing parenthesis?
>>> help(range)
Help on class range in module builtins:
class range(object)
| range(stop) -> range object
| range(start, stop[, step]) -> range object
|
| Return a virtual sequence of numbers from start to stop by step.
|
| Methods defined here:
|
| __contains__(self, key, /)
| Return key in self.
|
| __eq__(self, value, /)
| Return self==value.
...
It signifies the end of the positional only parameters, parameters you cannot use as keyword parameters. Before Python 3.8, such parameters could only be specified in the C API.
It means the key
argument to __contains__
can only be passed in by position (range(5).__contains__(3)
), not as a keyword argument (range(5).__contains__(key=3)
), something you can do with positional arguments in pure-python functions.
Also see the Argument Clinic documentation:
To mark all parameters as positional-only in Argument Clinic, add a
/
on a line by itself after the last parameter, indented the same as the parameter lines.
and the (very recent addition to) the Python FAQ:
A slash in the argument list of a function denotes that the parameters prior to it are positional-only. Positional-only parameters are the ones without an externally-usable name. Upon calling a function that accepts positional-only parameters, arguments are mapped to parameters based solely on their position.
The syntax is now part of the Python language specification, as of version 3.8, see PEP 570 – Python Positional-Only Parameters. Before PEP 570, the syntax was already reserved for possible future inclusion in Python, see PEP 457 - Syntax For Positional-Only Parameters.
Positional-only parameters can lead to cleaner and clearer APIs, make pure-Python implementations of otherwise C-only modules more consistent and easier to maintain, and because positional-only parameters require very little processing, they lead to faster Python code.
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