concurrent.futures does not throw exception when using try except-CodePudding

When using concurrent.futures.ThreadPoolExecutor() it doesn't throw an exception for try except.

For eg:

num = [1,2,3,4,5]
def div():
    for i in num:
        return i/0
    print('Done')

try:
    div()
except:
    print('Not Divisible by 0')

The above code prints the except part but the below code doesn't

num = [1,2,3,4,5]
def div(i):
    return i/0

try:
    with concurrent.futures.ThreadPoolExecutor() as executor:
        executor.map(div, num)
    print('Done')
except:
    print('Not Divisible by 0')

CodePudding user response：

executor.map does not raise the exception right away. Instead that exception will be raised when the value is retrieved from the iterator. For example try this,

>>> num = [1,2,3,4,5]
>>>
>>> def div(i):
...     return i/0
...
>>> import concurrent.futures
>>>
>>> with concurrent.futures.ThreadPoolExecutor() as executor:
...     result = executor.map(div, num)
...
>>> result # Not evaluated yet
<generator object Executor.map.<locals>.result_iterator at 0x0000019E60A36570>
>>> list(result) # This will raise the `ZeroDivisionError` exception

So to get the expected behavior, evaluate the return value of executor.map within the try block.