Question

以下是四个功能：

A（），B（）和A_B（）全部返回预期结果。另一方面，A_B_2（）失败，尽管基本相同。

我似乎无法弄清楚为什么尽管与A_B完全相同，A_B_2中的IF AND语句也会被区别对待。

def A(the_filter):
    print "start A()"
    for o in range(length):
        for x in range(length):
            if the_filter == "A" and x < 3 :
                print the_filter, o, x+1
            else:
                print the_filter, o, x-x
    return "end A()"

def B(the_filter):
    print "start B()"
    for o in range(length):
        for x in range(length):
            if the_filter == "B" and o != x :
                print the_filter, o, x
            else:
                print the_filter, "fail"
    return "end B()"

def A_B(the_filter):
    print "start A_B()"
    for o in range(length):
        for x in range(length):
            if the_filter == "A" :
                if x < 3 :
                    print the_filter, o, x+1
                else:
                    print the_filter, o, x-x
            if the_filter == "B" :
                if o != x :
                    print the_filter, o, x
                else:
                    print the_filter, "fail"
    return "end A_B()"

def A_B_2(the_filter):
    print "start A_B_2()"
    for o in range(length):
        for x in range(length):
            if the_filter == "A" and x < 3 :
                print the_filter, o, x+1
            else:
                print the_filter, o, x-x
            if the_filter == "B" and o != x :
                print the_filter, o, x
            else:
                print the_filter, "fail"
    return "A_B_2()"

length = 3
print A("A"), "\n"
print B("B"), "\n"
print A_B("A"), "\n"
print A_B("B"), "\n"
print A_B_2("A"), "\n"
print A_B_2("B"), "\n"

我得到的输出是：

start A()
A 0 1
A 0 2
A 0 3
A 1 1
A 1 2
A 1 3
A 2 1
A 2 2
A 2 3
end A() 

start B()
B fail
B 0 1
B 0 2
B 1 0
B fail
B 1 2
B 2 0
B 2 1
B fail
end B() 

start A_B()
A 0 1
A 0 2
A 0 3
A 1 1
A 1 2
A 1 3
A 2 1
A 2 2
A 2 3
end A_B() 

start A_B()
B fail
B 0 1
B 0 2
B 1 0
B fail
B 1 2
B 2 0
B 2 1
B fail
end A_B() 

start A_B_2()
A 0 1
A fail
A 0 2
A fail
A 0 3
A fail
A 1 1
A fail
A 1 2
A fail
A 1 3
A fail
A 2 1
A fail
A 2 2
A fail
A 2 3
A fail
A_B_2() 

start A_B_2()
B 0 0
B fail
B 0 0
B 0 1
B 0 0
B 0 2
B 1 0
B 1 0
B 1 0
B fail
B 1 0
B 1 2
B 2 0
B 2 0
B 2 0
B 2 1
B 2 0
B fail
A_B_2()

Answer 1

在您的代码中，Variable的以下部分：

A_B

不等同于if the_filter == "A" : if x < 3 : print the_filter, o, x+1 else: print the_filter, o, x-x的以下片段：

A_B_2

即如果if the_filter == "A" and x < 3 : print the_filter, o, x+1 else: print the_filter, o, x-x等于the_filter，则第一个版本将不执行任何操作（因为"B"计算为the_filter == "A"），而第二个版本将执行False分支（因为else计算为the_filter == "A" and x < 3）。

这导致例如出现在由False打印的第一行（B 0 0）上，与A_B_2("B")输出的内容相比较。

Answer 2

感谢Alex的反馈。（上图）经过一段时间的睡眠后，我想我已经把头包裹起来，你的回答是有道理的。

为了让A_B_2（）返回相同的输出A_B（），我需要用else替换elif，以确保在语句的第二部分仍然考虑the_filter 。因此：

def A_B_2(the_filter): print "start A_B_2()" for o in range(length): for x in range(length): if the_filter == "A" and x < 3 : print the_filter, o, x+1 elif the_filter == "A" : print the_filter, o, x-x if the_filter == "B" and o != x : print the_filter, o, x elif the_filter == "B": print the_filter, "fail" return "A_B_2()"

python：为什么我的是这个如果失败如此严重...

2 个答案: