如何定义嵌套参数？

问题描述：

我正在尝试将我的代码编译成 Python 3 模块。当我在 IDLE 中选择“运行模块”时，它运行良好，但当我尝试创建分发时收到以下语法错误：

File "/usr/local/lib/python3.2/dist-packages/simpletriple.py", line 9
    def add(self, (sub, pred, obj)):
                  ^
SyntaxError: invalid syntax

语法有什么问题？以下是完整代码：

import csv

class SimpleGraph:
    def __init__(self):
        self._spo = {}
        self._pos = {}
        self._osp = {}
    
    def add(self, (sub, pred, obj)):
        """
        Adds a triple to the graph.
        """
        self._addToIndex(self._spo, sub, pred, obj)
        self._addToIndex(self._pos, pred, obj, sub)
        self._addToIndex(self._osp, obj, sub, pred)
    
    def _addToIndex(self, index, a, b, c):
        """
        Adds a triple to a specified index.
        """
        if a not in index: index[a] = {b:set([c])}
        else:
            if b not in index[a]: index[a][b] = set([c])
            else: index[a][b].add(c)

    def remove(self, (sub, pred, obj)):
        """
        Remove a triple pattern from the graph.
        """
        triples = list(self.triples((sub, pred, obj)))
        for (delSub, delPred, delObj) in triples:
            self._removeFromIndex(self._spo, delSub, delPred, delObj)
            self._removeFromIndex(self._pos, delPred, delObj, delSub)
            self._removeFromIndex(self._osp, delObj, delSub, delPred)

    def _removeFromIndex(self, index, a, b, c):
        """
        Removes a triple from an index and clears up empty indermediate structures.
        """
        try:
            bs = index[a]
            cset = bs[b]
            cset.remove(c)
            if len(cset) == 0: del bs[b]
            if len(bs) == 0: del index[a]
        # KeyErrors occur if a term was missing, which means that it wasn't a valid delete:
        except KeyError:
            pass

    def triples(self, (sub, pred, obj)):
        """
        Generator over the triple store.
        Returns triples that match the given triple pattern. 
        """
        # check which terms are present in order to use the correct index:
        try:
            if sub != None: 
                if pred != None:
                    # sub pred obj
                    if obj != None:
                        if obj in self._spo[sub][pred]: yield (sub, pred, obj)
                    # sub pred None
                    else:
                        for retObj in self._spo[sub][pred]: yield (sub, pred, retObj)
                else:
                    # sub None obj
                    if obj != None:
                        for retPred in self._osp[obj][sub]: yield (sub, retPred, obj)
                    # sub None None
                    else:
                        for retPred, objSet in self._spo[sub].items():
                            for retObj in objSet:
                                yield (sub, retPred, retObj)
            else:
                if pred != None:
                    # None pred obj
                    if obj != None:
                        for retSub in self._pos[pred][obj]:
                            yield (retSub, pred, obj)
                    # None pred None
                    else:
                        for retObj, subSet in self._pos[pred].items():
                            for retSub in subSet:
                                yield (retSub, pred, retObj)
                else:
                    # None None obj
                    if obj != None:
                        for retSub, predSet in self._osp[obj].items():
                            for retPred in predSet:
                                yield (retSub, retPred, obj)
                    # None None None
                    else:
                        for retSub, predSet in self._spo.items():
                            for retPred, objSet in predSet.items():
                                for retObj in objSet:
                                    yield (retSub, retPred, retObj)
        # KeyErrors occur if a query term wasn't in the index, so we yield nothing:
        except KeyError:
            pass
        
    def value(self, sub=None, pred=None, obj=None):
        for retSub, retPred, retObj in self.triples((sub, pred, obj)):
            if sub is None: return retSub
            if pred is None: return retPred
            if obj is None: return retObj
            break
        return None

    def load(self, filename):
        f = open(filename, "rb")
        reader = csv.reader(f)
        for sub, pred, obj in reader:
            sub = unicode(sub, "UTF-8")
            pred = unicode(pred, "UTF-8")
            obj = unicode(obj, "UTF-8")
            self.add((sub, pred, obj))
        f.close()

    def save(self, filename):
        f = open(filename, "wb")
        writer = csv.writer(f)
        for sub, pred, obj in self.triples((None, None, None)):
            writer.writerow([sub.encode("UTF-8"), pred.encode("UTF-8"), obj.encode("UTF-8")])
        f.close()

if __name__ == "__main__":
    g = SimpleGraph()
    g.add(("blade_runner", "name", "Blade Runner"))
    g.add(("blade_runner", "name", "Blade Runner"))
    g.add(("blade_runner", "release_date", "June 25, 1982"))
    g.add(("blade_runner", "directed_by", "Ridley Scott"))

    print list(g.triples((None, None, None)))
    print list(g.triples(("blade_runner", None, None)))
    print list(g.triples(("blade_runner", "name", None)))
    print list(g.triples(("blade_runner", "name", "Blade Runner")))
    print list(g.triples(("blade_runner", None, "Blade Runner")))
    print list(g.triples((None, "name", "Blade Runner")))
    print list(g.triples((None, None, "Blade Runner")))

    print list(g.triples(("foo", "name", "Blade Runner")))
    print list(g.triples(("blade_runner", "foo", "Blade Runner")))
    print list(g.triples(("blade_runner", "name", "foo")))

解决方案 1：

PEP 3113解释了为什么 Python 3 中删除了“元组参数解包”这一功能。它还解释了如何移植使用它们的代码。在这种情况下，您需要更改如下函数：

def add(self, (sub, pred, obj)):
    self._addToIndex(self._spo, sub, pred, obj)
    self._addToIndex(self._pos, pred, obj, sub)
    self._addToIndex(self._osp, obj, sub, pred)

转换为将元组作为单个参数传递并手动解包的版本：

def add(self, sub_pred_obj):
    sub, pred, obj = sub_pred_obj
    self._addToIndex(self._spo, sub, pred, obj)
    self._addToIndex(self._pos, pred, obj, sub)
    self._addToIndex(self._osp, obj, sub, pred)

对于lambda函数，您不能使用赋值来解包。最好的解决方案通常是不解包。例如，更改此代码：

lambda (x, y): (y, x)

…变成这样：

lambda xy: (xy[1], xy[0])

对于复杂的功能，这可能会变得很难看 - 但是对于复杂的功能，您可能无论如何都想要def它们。

值得注意的是，通过、或运行代码2to3会modernize在futurize和中发现这个问题def，lambda并提出以下解决方案：

$ echo 'lambda (x,y): (y,x)' | 2to3 -
--- <stdin> (original)
+++ <stdin> (refactored)
@@ -1 +1 @@
-lambda (x,y): (y,x)
+lambda x_y: (x_y[1],x_y[0])

$ echo -e 'def foo((x,y)):
    return (y,x)
' | 2to3 -
--- <stdin> (original)
+++ <stdin> (refactored)
@@ -1 +1 @@
-def foo((x,y)):
+def foo(xxx_todo_changeme):
+    (x,y) = xxx_todo_changeme

如果您尝试将 Python 2.x 代码移植到 3.x（或双版本代码）并且不了解这两种语言，那么您几乎肯定会想要使用其中一种工具（或包装它们的 IDE 插件）来提供帮助。（尽管您可能不想按原样使用它的输出。）