<p>假设您想要的是“在第一次函数调用时只初始化一次的变量”,那么在Python语法中没有这样的东西。但也有办法得到类似的结果:</p>
<p>1-使用全局。注意,在Python中,“global”真正的意思是“模块的global”,而不是“进程的global”:</p>
<pre><code>_number_of_times = 0
def yourfunc(x, y):
global _number_of_times
for i in range(x):
for j in range(y):
_number_of_times += 1
</code></pre>
<p>2-将代码包装到类中并使用类属性(即:所有实例共享的属性)。以下内容:</p>
<pre><code>class Foo(object):
_number_of_times = 0
@classmethod
def yourfunc(cls, x, y):
for i in range(x):
for j in range(y):
cls._number_of_times += 1
</code></pre>
<p>注意,我使用了一个<code>classmethod</code>,因为这个代码片段不需要来自实例的任何东西</p>
<p>3-将代码包装到类中,使用实例属性并为方法提供快捷方式:</p>
<pre><code>class Foo(object):
def __init__(self):
self._number_of_times = 0
def yourfunc(self, x, y):
for i in range(x):
for j in range(y):
self._number_of_times += 1
yourfunc = Foo().yourfunc
</code></pre>
<p>4-编写可调用类并提供快捷方式:</p>
<pre><code>class Foo(object):
def __init__(self):
self._number_of_times = 0
def __call__(self, x, y):
for i in range(x):
for j in range(y):
self._number_of_times += 1
yourfunc = Foo()
</code></pre>
<p>4之二-使用类属性和元类</p>
<pre><code>class Callable(type):
def __call__(self, *args, **kw):
return self._call(*args, **kw)
class yourfunc(object):
__metaclass__ = Callable
_numer_of_times = 0
@classmethod
def _call(cls, x, y):
for i in range(x):
for j in range(y):
cls._number_of_time += 1
</code></pre>
<p>5-在模块导入时“创造性地”使用仅实例化一次的函数默认参数:</p>
<pre><code>def yourfunc(x, y, _hack=[0]):
for i in range(x):
for j in range(y):
_hack[0] += 1
</code></pre>
<p>还有其他一些可能的解决方案/黑客,但我想你现在已经了解了大局。</p>
<p>编辑:鉴于op的澄清,即“假设你有一个带有默认参数的递归函数,但如果有人真的试图给你的函数再加一个参数,那可能是灾难性的”,看起来op真正想要的是:</p>
<pre><code># private recursive function using a default param the caller shouldn't set
def _walk(tree, callback, level=0):
callback(tree, level)
for child in tree.children:
_walk(child, callback, level+1):
# public wrapper without the default param
def walk(tree, callback):
_walk(tree, callback)
</code></pre>
<p>顺便说一句,这证明我们确实还有另一个XY问题。。。</p>