Python语法糖：函数arg别名

crunk1 发表于 Dev

笨拙1

别名函数args有语法吗？如果没有，是否有任何PEP建议？我不是编程语言理论家，所以我的看法可能不为人所知，但是我认为实现某种函数arg别名可能会有用。

我正在对libcloud进行一些更改，我的想法将帮助我避免在更改API时破坏其他内容。

例如，假设我正在重构，并想将函数arg'foo'重命名为'bar'：

原版的：

def fn(foo):
    <code (using 'foo')>

我可以：

def fn(foo, bar=None):
    if foo and bar:
        raise Exception('Please use foo and bar mutually exclusively.')
    bar = foo or bar
    <code (using 'bar')>

# But this is undesirable because it changes the method signature to allow
# a new parameter slot.
fn('hello world', 'goodbye world')

我未完善的语法糖想法：

def fn(bar|foo|baz):
    # Callers can use foo, bar, or baz, but only the leftmost arg name
    # is used in the method code block. In this case, it would be bar.
    # The python runtime would enforce mutual exclusion between foo,
    # bar, and baz.
    <code (using 'bar')>

# Valid uses:
fn(foo='hello world')
fn(bar='hello world')
fn(baz='hello world')
fn('hello world')

# Invalid uses (would raise some exception):
fn(foo='hello world', bar='goodbye world')
fn('hello world', baz='goodbye world')

落下

也许没有，您可以使用装饰器（如上所示）或第一手使用kwargs来做到这一点：

def fn (**kw):
    arg = kw.get("foo") or kw.get("bar") or kw.get("baz")
    if arg==None: raise TypeError, "foo nor bar nor baz given az argument"
    print arg

Here the order of precedence is: "if foo exists, arg is foo. if it doesn't but bar exists, arg is bar, if neither foo nor bar exists, the arg is baz. If baz doesn't, i.e. all 3 are missing, arg is None.

Of course, you may check whether either one exists and force the mutual exclusion, but I don't see why would you need such a thing.

You are clever and you will never pass them in together. Even if you do, some will be ignored.

您也可以使用可调用对象来执行此操作，甚至可以在运行时将语法和行为引入解释器。

但是我认为，将其作为有效的Python语法引入并不是Python的，即使有PEP，也永远不会发生。

如您所见，您可以执行所需的操作而不会弄脏Python语法。

我并不是说您的例子在语法上不明确，只是不必要。

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