Python 条件语句显示错误结果 (32==0) --> True

Question

为什么python在下面的代码中显示(32 == 0)

当我测试以下代码时给出了一个奇怪的结果

while not stop:
    results = pyautogui.locateAllOnScreen('background data/test.png', confidence = 0.9)
    print(len(list(results)))
    print(len(list(results)) == 0)
    if len(list(results)) == 0:
        print('exit loop')
        break

上面代码的结果是

32
True
exit loop

len(list(results))给出 的输出32: int，但与 比较时0: int，返回 True

Answer 1

pyautogui.locateAllOnScreen返回一个生成器，您在最初打印长度时会耗尽该生成器。要解决此问题，请转换results为列表或删除调试语句。

这就是正在发生的事情：

# results is a generator like below
results = (i for i in range(2))

# by calling list on the generator, we consume/exhaust it.
print(len(list(results)))
# output: 2

# if we try to consume again, the generator is empty
print(len(list(results)) == 0)
# output: True, as the len(list(results)) is 0

你可以这样做：

# create a generator again
results = (i for i in range(2))

# consume it by converting generator to list once 
results_list = list(results)

print(len(results_list))
# output: 2

print(len(results_list) == 0)
# output: False, as the len(results_list) is 2