参数是通过引用传递还是通过值传递？如何通过引用传递，以便下面的代码输出“Changed”而不是“Original”？
class PassByReference:
def __init__(self):
self.variable = 'Original'
self.change(self.variable)
print(self.variable)
def change(self, var):
var = 'Changed'
另请参阅：为什么函数可以修改调用者感知的某些参数，而不能修改其他参数？
当前回答
由于字典是通过引用传递的，所以可以使用dict变量在其中存储任何引用的值。
# returns the result of adding numbers `a` and `b`
def AddNumbers(a, b, ref): # using a dict for reference
result = a + b
ref['multi'] = a * b # reference the multi. ref['multi'] is number
ref['msg'] = "The result: " + str(result) + " was nice!"
return result
number1 = 5
number2 = 10
ref = {} # init a dict like that so it can save all the referenced values. this is because all dictionaries are passed by reference, while strings and numbers do not.
sum = AddNumbers(number1, number2, ref)
print("sum: ", sum) # the returned value
print("multi: ", ref['multi']) # a referenced value
print("msg: ", ref['msg']) # a referenced value
其他回答
由于您的示例恰好是面向对象的，因此可以进行以下更改以获得类似的结果：
class PassByReference:
def __init__(self):
self.variable = 'Original'
self.change('variable')
print(self.variable)
def change(self, var):
setattr(self, var, 'Changed')
# o.variable will equal 'Changed'
o = PassByReference()
assert o.variable == 'Changed'
由于字典是通过引用传递的，所以可以使用dict变量在其中存储任何引用的值。
# returns the result of adding numbers `a` and `b`
def AddNumbers(a, b, ref): # using a dict for reference
result = a + b
ref['multi'] = a * b # reference the multi. ref['multi'] is number
ref['msg'] = "The result: " + str(result) + " was nice!"
return result
number1 = 5
number2 = 10
ref = {} # init a dict like that so it can save all the referenced values. this is because all dictionaries are passed by reference, while strings and numbers do not.
sum = AddNumbers(number1, number2, ref)
print("sum: ", sum) # the returned value
print("multi: ", ref['multi']) # a referenced value
print("msg: ", ref['msg']) # a referenced value
我通常使用的一个简单技巧是将其包装在列表中：
def Change(self, var):
var[0] = 'Changed'
variable = ['Original']
self.Change(variable)
print variable[0]
（是的，我知道这可能很不方便，但有时这样做很简单。）
或者，你可以使用看起来像这样的ctypes
import ctypes
def f(a):
a.value=2398 ## resign the value in a function
a = ctypes.c_int(0)
print("pre f", a)
f(a)
print("post f", a)
因为a是一个c整数，而不是python整数，并且通过引用传递。然而，你必须小心，因为可能会发生奇怪的事情，因此不建议
我分享了另一种有趣的方式，让人们通过一个方便的工具来理解这个主题——基于@Mark Ransom传递可变列表的示例，可视化巨蟒代码执行
随便玩玩，你就会明白的。
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