如果语句未命中，则继续断点 [英] Breakpoint on continue in if statement not hit

问题描述

在下面的代码中，a 和 b 都是生成器函数的输出，可以计算为 None 或有一个值.

In the following code, both a and b are outputs of generator functions, and could evaluate to None or have a value.

def testBehaviour(self):
  a = None
  b = 5

  while True:
    if not a or not b:
      continue
    print('blaat')

如果我在带有 continue 语句的行和带有 print 语句的行上放置断点(使用 Visual Studio Code)，则两者都不会命中.print 语句没有被调用，循环只是按预期无限期地运行，但我希望断点被命中.

If I put breakpoints (using Visual Studio Code) on the line with the continue statement, and the line with the print statement, neither is hit. The print statement is not called, and the loop just keeps running indefinitely as expected, but I would expect that breakpoints are hit.

如果我将代码更改为以下之一:

If I change the code to one of the following:

def testBehaviour(self):
  a = None
  b = 5

  while True:
    if not a:
      continue
    print('blaat')

或:

def testBehaviour(self):
  a = None
  b = 5

  while True:
    if not a or not b:
      c = 'dummy'
      continue
    print('blaat')

再次在带有 continue 和 print 语句的行上放置断点，断点被命中.

And again place breakpoints on the lines with the continue and print statements, the breakpoints are hit.

谁能告诉我为什么没有命中断点?这似乎不仅仅发生在 Visual Studio Code 中，因为我们的代码覆盖工具还指出未调用 continue 语句.

Can anyone tell me why the breakpoints are not hit? It seems to not happen only in Visual Studio Code, because our code-coverage tool also states that the continue statement was not called.

这是在 32 位 Windows 7 上的 python 2.7 上.

This is on python 2.7 on Windows 7, 32 bit.

推荐答案

操作码中有优化，编译器识别if expr: continue.

There is an optimization in the opcodes, the compiler recognizes the if expr: continue.

当使用if not a or not b:

 11          12 SETUP_LOOP              35 (to 50)
        >>   15 LOAD_GLOBAL              1 (True)
             18 POP_JUMP_IF_FALSE       49

 12          21 LOAD_FAST                1 (a)
             24 UNARY_NOT
             25 POP_JUMP_IF_TRUE        15
             28 LOAD_FAST                2 (b)
             31 UNARY_NOT
             32 POP_JUMP_IF_FALSE       41

 13          35 JUMP_ABSOLUTE           15
             38 JUMP_FORWARD             0 (to 41)

 14     >>   41 LOAD_CONST               2 ('blaat')
             44 PRINT_ITEM
             45 PRINT_NEWLINE
             46 JUMP_ABSOLUTE           15
        >>   49 POP_BLOCK
        >>   50 LOAD_CONST               0 (None)
             53 RETURN_VALUE

如果 not a 为真，25 POP_JUMP_IF_TRUE 15 行将跳回到 while 循环的开头(第 15 行).它永远不会到达 continue 语句的行 35 JUMP_ABSOLUTE 15

The line 25 POP_JUMP_IF_TRUE 15 jumps back to the start of the while loop (line 15) if not a is true. It never reaches the line of the continue statement 35 JUMP_ABSOLUTE 15

如果您切换 a 和 b 的值，此测试用例有效.

If you switch the values of a and b this test case works.

如果您将测试表达式重写为 if not ( a 和 b ): 您会得到以下操作码

If you rewrite the test expression to if not ( a and b ): you get the following opcodes

 11          12 SETUP_LOOP              33 (to 48)
        >>   15 LOAD_GLOBAL              1 (True)
             18 POP_JUMP_IF_FALSE       47

 12          21 LOAD_FAST                1 (a)
             24 JUMP_IF_FALSE_OR_POP    30
             27 LOAD_FAST                2 (b)
        >>   30 POP_JUMP_IF_TRUE        39

 13          33 JUMP_ABSOLUTE           15
             36 JUMP_FORWARD             0 (to 39)

 14     >>   39 LOAD_CONST               2 ('blaat')
             42 PRINT_ITEM
             43 PRINT_NEWLINE
             44 JUMP_ABSOLUTE           15
        >>   47 POP_BLOCK
        >>   48 LOAD_CONST               0 (None)
             51 RETURN_VALUE

这总是有效并且速度更快.not 操作优化为跳转测试语句

And that always works and is faster. The not operations are optimized into the jump test statements

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