Pythonic在for循环中使用'else'的方法

我几乎没有注意到在for循环中使用else的python程序.

我最近使用它在退出时根据循环变量条件执行操作; 因为它在范围内.

在for循环中使用else的pythonic方法是什么？有没有值得注意的用例？

而且,是的.我不喜欢使用break语句.我宁愿将循环条件设置为复杂的.如果我不喜欢使用break语句,我能从中获得任何好处吗？

值得注意的是,自语言开始以来,for循环有一个else,这是第一个版本.

有什么比PyPy更pythonic？

看一下我在c​​types_configure/configure.py第284行开始发现的内容:

    for i in range(0, info['size'] - csize + 1, info['align']):
        if layout[i:i+csize] == [None] * csize:
            layout_addfield(layout, i, ctype, '_alignment')
            break
    else:
        raise AssertionError("unenforceable alignment %d" % (
            info['align'],))

在这里,从pypy/annotation中的第425行/ annrpython.py(clicky)

if cell.is_constant():
    return Constant(cell.const)
else:
    for v in known_variables:
        if self.bindings[v] is cell:
            return v
    else:
        raise CannotSimplify

在pypy/annotation/binaryop.py中,从第751行开始:

def is_((pbc1, pbc2)):
    thistype = pairtype(SomePBC, SomePBC)
    s = super(thistype, pair(pbc1, pbc2)).is_()
    if not s.is_constant():
        if not pbc1.can_be_None or not pbc2.can_be_None:
            for desc in pbc1.descriptions:
                if desc in pbc2.descriptions:
                    break
            else:
                s.const = False    # no common desc in the two sets
    return s

pypy/annotation/classdef.py中的非单行,从第176行开始:

def add_source_for_attribute(self, attr, source):
    """Adds information about a constant source for an attribute.
    """
    for cdef in self.getmro():
        if attr in cdef.attrs:
            # the Attribute() exists already for this class (or a parent)
            attrdef = cdef.attrs[attr]
            s_prev_value = attrdef.s_value
            attrdef.add_constant_source(self, source)
            # we should reflow from all the reader's position,
            # but as an optimization we try to see if the attribute
            # has really been generalized
            if attrdef.s_value != s_prev_value:
                attrdef.mutated(cdef) # reflow from all read positions
            return
    else:
        # remember the source in self.attr_sources
        sources = self.attr_sources.setdefault(attr, [])
        sources.append(source)
        # register the source in any Attribute found in subclasses,
        # to restore invariant (III)
        # NB. add_constant_source() may discover new subdefs but the
        #     right thing will happen to them because self.attr_sources
        #     was already updated
        if not source.instance_level:
            for subdef in self.getallsubdefs():
                if attr in subdef.attrs:
                    attrdef = subdef.attrs[attr]
                    s_prev_value = attrdef.s_value
                    attrdef.add_constant_source(self, source)
                    if attrdef.s_value != s_prev_value:
                        attrdef.mutated(subdef) # reflow from all read positions

稍后在同一个文件中,从第307行开始,这是一个带有启发性注释的示例:

def generalize_attr(self, attr, s_value=None):
    # if the attribute exists in a superclass, generalize there,
    # as imposed by invariant (I)
    for clsdef in self.getmro():
        if attr in clsdef.attrs:
            clsdef._generalize_attr(attr, s_value)
            break
    else:
        self._generalize_attr(attr, s_value)

如果你有一个for循环,你真的没有任何条件声明.因此,如果您想中止,那么休息是您的选择,然后可以完美地处理您不满意的情况.

for fruit in basket:
   if fruit.kind in ['Orange', 'Apple']:
       fruit.eat()
       break
else:
   print 'The basket contains no desirable fruit'