Exception not thrown in python3

[ONEoo7]

Why does the call of inclusive_range() at line 71 not throw an exception and instead it prints "Test FAILED"?

def test(*args):
    print(type(args))
    print(len(args))
    if len(args) == 1:
        raise ValueError("too many args, [1, 2]")

def inclusive_range(*args):
    numargs = len(args)
    print(numargs)
    if numargs < 1:
        raise ValueError("number of args less than 1, needed interval [1, 3]")
    elif numargs == 1:
        start = 0
        stop = args[0]
        step = 1
    elif numargs == 2:
        (start, stop) = args
        step = 1
    elif numargs == 3:
        (start, stop, step) = args
    else:
        raise ValueError("number of args greater than 3, needed interval [1, 3]")
    i = start
    while i <= stop:
        yield i
        i += step

# test cases
def main():
    # valid 1 arg
    for i in inclusive_range(20):
        print(i, end=' ')
    print()
        
    # valid 2 args
    for i in inclusive_range(0, 21):
        print(i, end=' ')
    print()
    
    # valid 3 args
    for i in inclusive_range(0, 22, 2):
        print(i, end=' ')
    print()
    
    # invalid 0 args
    try:
        myRange = inclusive_range()
        for i in myRange:
            print(i)
    except ValueError as e:
        print(e)
    except:
        print("Unknown exception occured")
    else:
        print("Test FAILED")
        
    # invalid 4 args
    try:
        myRange = inclusive_range(1, 2, 3, 4)
        for i in myRange:
            print(i)
    except ValueError as e:
        print(e)
    except:
        print("Unknown exception occured")
    else:
        print("Test FAILED")
        
    # invalid 5 args, warning myRange not used (possibly optimized out by python)
    try:
        myRange = inclusive_range(1, 2, 3, 4, 5)
    except ValueError as e:
        print(e)
    except:
        print("Unknown exception occured")
    else:
        print("Test FAILED")
    
    test()
    try:
        test(1)
    except ValueError as e:
        print(e)
    else:
        print("everything is fine here, move along.")


if __name__ == "__main__": main()

[wavic]

Else block will be executed no matter what. Or it was finally?!...

Well, the else block will be executed if there was no exception.

[Larz60+]

surround your code with:

try:
    ...
except Exception as ex:
    # todo -- Use tkinter.messagebox here
    template = "An exception of type {0} occurred. arguments: \n{1!r}"
    message = template.format(type(ex).__name__, ex.args)
    print(message)
    raise Exception

to see what's being thrown

[ONEoo7]

I am now learning python3. From what I remember it was finally that was always executed.
I have made two different versions of the same function.
1st version is generator function
2nd version is generator object

See both versions here:
https://gist.github.com/ONEoo7

[wavic]

Finally will be executed in all circumstances. Else will be executed before finally  if there is no exception in the try block.

[zivoni]

There was no exception, so else block was executed. Your inclusive_range is not a standard function, but generator function and call of inclusive_range() does not execute any code from inclusive_range, only returns generator object (iterator). You need to use next() on it (or directly call .__next__() ) to execute code from its body.

[ONEoo7]

Ok, so just calling the function does not actually make it behave like a normal c/c++ function or method. It returns immediately with a generator object(seen with the debugger). When used in a for loop or manually calling .__next__() on the returned generator object will actually call the function and behave as expected, throw the exception in this case.

Thank you @zivoni.

[snippsat]

When used in a for loop or manually calling .__next__() on the returned generator object will actually call the function and behave as expected, throw the exception in this case.

Yes,and a generator run to StopIteration so that what you catch.
Eg:

def yrange(n):
    i = 0
    while i < n:
        yield i
        i += 1

>>> n = yrange(3)
>>> n
<generator object yrange at 0x02A4C3A0>
>>> next(n)
0
>>> next(n)
1
>>> next(n)
2
>>> next(n)
Traceback (most recent call last):
  File "<string>", line 301, in runcode
  File "<interactive input>", line 1, in <module>
StopIteration

A lot more build in stuff like range, map, zip, filter... ect has become generator/iterables in Python 3.x.
This conserve space rather than producing a result list all at once in memory.

It's a powerful concept as a example can slice in and take out the only part that needed.

>>> from itertools import islice
>>> g = (i for i in range(100))
>>> g
<generator object <genexpr> at 0x0124E4B8>
>>> list(islice(g, 50, 55))
[50, 51, 52, 53, 54]

So here get only Fibonacci from 35 to 40 executed.

from itertools import islice

def fib_gen():
    a, b = 1, 1
    while True:
        yield a
        a, b = b, a + b 

>>> list(islice(fib_gen(), 35, 40))
[14930352, 24157817, 39088169, 63245986, 102334155]