Python - 奇怪/意外的行为 - 运算符的优先级

Question

我最近对 ​​python 生成器进行了一些试验，我遇到了以下奇怪的行为，我很想知道为什么会发生这种情况以及发生了什么:

def generating_test(n): 
    for a in range(n): 
        yield "a squared is %s" % a*a # Notice instead of a**2 we have written a*a

for asquare in generating_test(3): 
    print asquare 

输出:

a squared is 1
a squared is 2a squared is 2

与生成预期输出的以下脚本相比:

def generating_test(n): 
    for a in range(n): 
        yield "a squared is %s" % a**2 # we use the correct a**2 here

for asquare in generating_test(3): 
    print asquare 

输出:

a squared is 0
a squared is 1
a squared is 4

Answer 1

这与生成器没有任何关系:

>>> a = 2
>>> "a squared is %s" % a
'a squared is 2'
>>> ("a squared is %s" % a)*a
'a squared is 2a squared is 2'
>>> "a squared is %s" % a*a
'a squared is 2a squared is 2'
>>> "a squared is %s" % (a*a)
'a squared is 4'

% 运算在乘法之前执行，使用字符串和第一个 a 作为参数。您的 a**2 之所以有效，是因为以 a 和 2 作为参数的 ** op 在 %。