元组切片 [英] Tuple slices
问题描述
为什么切片元组会返回一个新元组而不是现有元组的视图，因为
元组是不可变的？我最后编写了一个自定义的ImmutableSequence类来执行此操作，但是我想知道为什么它没有为元组实现。
George
George Sakkis写道：
为什么切片元组会返回一个新的元组而不是现有元组的视图，给定
元组是不可变的吗？
真的吗？
a = 1,2,3
b = a [：]
a是b
True
< / F>
Fredrik Lundh写道：George Sakkis写道：
为什么切片元组会返回一个新元组而不是现有元组的视图，因为
元组是不可变的？
真的吗？
a = 1,2,3
b = a [：]
a是b
True
我的印象是完整的元组副本实际上并没有复制，但是这可能是一个元组子集的切片。不完全确定如何测试这个，但是：
py> a = 1,2,3
py> a [：2]是[：2]
False
所以_something_至少在两个切片之间是不同的......
Steve
2005年1月24日星期一18:45:46 +0100
" Fredrik Lundh" < FR ***** @ pythonware.com>写道：
George Sakkis写道：
为什么切片元组会返回一个新的元组而不是现有的视图
一，鉴于元组是不可变的吗？
真的吗？
嗯......好像这个案例已经过优化，可以返回原来的元组
只是递增其引用计数并返回
tupleobject.c，330-335
if（ilow == 0&& ; ihigh == a-> ob_size&& PyTuple_CheckExact（a））{
Py_INCREF（a）;
return（PyObject *）a;
}
a = 1,2,3
b = a [：]
a是b
真的
< / F>
-
http://mail.python.org/mailman/listinfo/python-list
Why does slicing a tuple returns a new tuple instead of a view of the existing one, given that
tuples are immutable ? I ended up writing a custom ImmutableSequence class that does this, but I
wonder why it is not implemented for tuples.
George解决方案George Sakkis wrote:
Why does slicing a tuple returns a new tuple instead of a view of the existing one, given that
tuples are immutable ?
really?
a = 1, 2, 3
b = a[:]
a is b
True
</F>
Fredrik Lundh wrote:George Sakkis wrote:Why does slicing a tuple returns a new tuple instead of a view of the existing one, given that
tuples are immutable ?
really?a = 1, 2, 3
b = a[:]
a is b
True
My impression was that full tuple copies didn''t actually copy, but that
slicing a subset of a tuple might. Not exactly sure how to test this, but:
py> a = 1, 2, 3
py> a[:2] is a[:2]
False
So _something_ at least is different between the two slices...
Steve
On Mon, 24 Jan 2005 18:45:46 +0100
"Fredrik Lundh" <fr*****@pythonware.com> wrote:
George Sakkis wrote:Why does slicing a tuple returns a new tuple instead of a view of
the existing one, given that tuples are immutable ?
really?
Well... seems like this case is optimized to return the original tuple
just incrementing its reference count and returning
tupleobject.c, 330-335
if (ilow == 0 && ihigh == a->ob_size && PyTuple_CheckExact(a)) {
Py_INCREF(a);
return (PyObject *)a;
}
a = 1, 2, 3
b = a[:]
a is b
True
</F>
--
http://mail.python.org/mailman/listinfo/python-list
这篇关于元组切片的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
