Question

所以Python是通过引用传递的。总是。但是整数，字符串和元组之类的对象，即使传递给函数，也无法更改（因此它们被称为不可变）。这是一个例子。

def foo(i, l):
  i = 5 # this creates a new variable which is also called i
  l = [1, 2] # this changes the existing variable called l

i = 10
l = [1, 2, 3]
print(i)
# i = 10
print(l)
# l = [1, 2, 3]
foo(i, l)
print(i)
# i = 10 # variable i defined outside of function foo didn't change
print(l)
# l = [1, 2] # l is defined outside of function foo did change

因此，您可以看到整数对象是不可变的，而列表对象是可变的。

在Python中使用不可变对象的原因是什么？如果所有对象都是可变的，那么像Python这样的语言会有什么优点和缺点？

Answer 1

您的示例不正确。 l 未在<{1}}范围之外进行更改。 foo()内的i和l是指向新对象的新名称。

foo()

现在，如果您将Python 2.7.10 (default, Aug 22 2015, 20:33:39) [GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.59.1)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> def foo(i, l): ... i = 5 # this creates a local name i that points to 5 ... l = [1, 2] # this creates a local name l that points to [1, 2] ... >>> i = 10 >>> l = [1, 2, 3] >>> print(i) 10 >>> print(l) [1, 2, 3] >>> foo(i, l) >>> print(i) 10 >>> print(l) [1, 2, 3]更改为变异foo()，那就是另一个故事

Python 3的例子是相同的

>>> def foo(i, l):
...     l.append(10)
...
>>> foo(i, l)
>>> print(l)
[1, 2, 3, 10]

为什么Python中存在不可变对象？

1 个答案: