Python 中的冒号等于 (:=) 是什么意思？
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What does colon equal (:=) in Python mean?
提问by Julio
What does the :=operand mean, more specifically for Python?
:=操作数是什么意思，更具体地说是对 Python 而言？
Can someone explain how to read this snippet of code?
有人可以解释如何阅读这段代码吗？
node := root, cost = 0
frontier := priority queue containing node only
explored := empty set
采纳答案by Mike McMahon
Updated answer
更新答案
In the context of the question, we are dealing with pseudocode, but starting in Python 3.8, :=is actually a valid operator that allows for assignment of variables within expressions:
在问题的上下文中，我们正在处理伪代码，但从Python 3.8 开始，:=实际上是一个有效的运算符，允许在表达式中分配变量：
# Handle a matched regex
if (match := pattern.search(data)) is not None:
# Do something with match
# A loop that can't be trivially rewritten using 2-arg iter()
while chunk := file.read(8192):
process(chunk)
# Reuse a value that's expensive to compute
[y := f(x), y**2, y**3]
# Share a subexpression between a comprehension filter clause and its output
filtered_data = [y for x in data if (y := f(x)) is not None]
See PEP 572for more details.
有关更多详细信息，请参阅PEP 572。
Original Answer
原答案
What you have found is pseudocode
你发现的是伪代码
Pseudocodeis an informal high-level description of the operating principle of a computer program or other algorithm.
伪代码是对计算机程序或其他算法的操作原理的非正式高级描述。
:=is actually the assignment operator. In Python this is simply =.
:=实际上是赋值运算符。在 Python 中，这只是=.
To translate this pseudocode into Python you would need to know the data structures being referenced, and a bit more of the algorithm implementation.
要将这个伪代码翻译成 Python，您需要知道被引用的数据结构，以及更多的算法实现。
Some notes about psuedocode:
关于伪代码的一些说明：
:=is the assignment operator or=in Python=is the equality operator or==in Python- There are certain styles, and your mileage may vary:
:=是赋值运算符还是=在 Python 中=是相等运算符还是==在 Python 中- 有某些款式，您的里程可能会有所不同：
Pascal-style
帕斯卡式
procedure fizzbuzz
For i := 1 to 100 do
set print_number to true;
If i is divisible by 3 then
print "Fizz";
set print_number to false;
If i is divisible by 5 then
print "Buzz";
set print_number to false;
If print_number, print i;
print a newline;
end
C-style
C型
void function fizzbuzz
For (i = 1; i <= 100; i++) {
set print_number to true;
If i is divisible by 3
print "Fizz";
set print_number to false;
If i is divisible by 5
print "Buzz";
set print_number to false;
If print_number, print i;
print a newline;
}
Note the differences in brace usage and assignment operator.
请注意大括号用法和赋值运算符的差异。
回答by chadlagore
回答by Clément
The code in the question is pseudo-code; there, :=represents assignment.
问题中的代码是伪代码；在那里，:=代表赋值。
For future visitors, though, the following might be more relevant: the next version of Python (3.8) will gain a new operator, :=, allowing assignment expressions(details, motivating examples, and discussion can be found in PEP 572, which was provisionally accepted in late June 2018).
但是，对于未来的访问者，以下内容可能更相关：Python 的下一个版本 (3.8) 将获得一个新的运算符:=，允许赋值表达式（详细信息、激励示例和讨论可以在PEP 572 中找到，它被暂时接受2018 年 6 月下旬）。
With this new operator, you can write things like these:
使用这个新运算符，您可以编写如下内容：
if (m := re.search(pat, s)):
print m.span()
else if (m := re.search(pat2, s):
…
while len(bytes := x.read()) > 0:
… do something with `bytes`
[stripped for l in lines if len(stripped := l.strip()) > 0]
instead of these:
而不是这些：
m = re.search(pat, s)
if m:
print m.span()
else:
m = re.search(pat2, s)
if m:
…
while True:
bytes = x.read()
if len(bytes) <= 0:
return
… do something with `bytes`
[l for l in (l.stripped() for l in lines) if len(l) > 0]
回答by Wera
Happy 3.8 Release on 14th of October!
10 月 14 日 3.8 发布快乐！
There is new syntax
:=that assigns values to variables as part of a larger expression. It is affectionately known as “the walrus operator” due to its resemblance to the eyes and tusks of a walrus.In this example, the assignment expression helps avoid calling
len()twice:if (n := len(a)) > 10: print(f"List is too long ({n} elements, expected <= 10)")
有新的语法
:=可以将值分配给变量作为更大表达式的一部分。由于它与海象的眼睛和象牙相似，因此被亲切地称为“海象操作员”。在这个例子中，赋值表达式有助于避免调用
len()两次：if (n := len(a)) > 10: print(f"List is too long ({n} elements, expected <= 10)")
