Error in python

Question

Can someone help me with my bug in my code? This is the part:
#exceptions
something = input() # take an input

try: # do something with the input
something = (int(something)) # if it's not a number it's a ValueError
print(something)
print(someting) # make a mistake
print(movies[something])
except ValueError: # if input isn't a number
print("type in a number")
except IndexError: # if number is too high
print("number must be under 6")
except NameError: # if I used a wrong variable
print("something is wrong with something ;)")

try: # do something with the input
print(something + 1) # if it's not a number it's a TypeError
print(something # another mistake
except TypeError: # if input isn't a number
print("type in a number")
except SyntaxError:
print("There's a bug in the code")

https://sololearn.com/compiler-playground/chE9gTsNZeHl/?ref=app

Answer 1

Jakob
oh, I didn't realize it was intentional.

The problem is that syntax errors are caught when the code is being parsed, so the rest of the code do not get executed if it's thrown.

One way to get around this is to execute it separately. Here is a warranted use case for the eval or exec function.

change line 128 to:

exec("print(something # another mistake")

or

eval("print(something ") # another mistake

Answer 2

The first try-except block already raises an exception, and the code is no further interpreted. What behavior do you expect for your code?

Answer 3

As I understand it, it works like this:

The SyntaxError is raised before the code is executed (when the code is parsed, that is: when it is checked if it is a valid code).

The NameError is only checked at runtime, when the code is executed.

So, the SyntaxError has a special role compared to the other Errors. Whenever a SyntaxError is encomluntered, the code will not be executed at all, and hence, other non-syntactical errors won't be raised.

Answer 4

Don't delete it :)

But I'm afraid you can show the SyntaxError in the same demo as the other errors. Perhaps you could make an extra script to explain how SyntaxErrors are handled?

Answer 5

I assume that the syntax error has higher precedence than the name error and that's why we're sent to line 129 straight away. I will need to have a closer look when I am free!

Answer 6

Thanks! Is there another way to do what I want or should I just delete it?

Answer 7

Bob_Li
I was rather referring to the demo itself: If the SyntaxError doesn't allow executing the script at all, a demo on errors and exceptions should veridically show this instead of raising exceptions just for the sake of raising exceptions because then it doesn't represent the intended use-case. (Just my thoughts; I respect your approach to it.)

Answer 8

I would like to trigger all except blocks for the demo.

Answer 9

Thank you very much! I can wait 😀

Answer 10

Jakob

you forgot to close the parenthesis for print on line 128

128 print(something # another mistake
^ mistake here
should be:

128 print(something) # another mistake

it is a syntax error, but the error mesage pointed to the wrong part ....

Answer 11

I know, I wanted to trigger a Syntax Error. But I made it in a try except block

Answer 12

Jakob
Here's how I would write the exceptions section so everything is displayed,.
Use separate try-except blocks with different values for something.:

#exceptions

something = 'x'
try: # convert to int
print(int(something))
except ValueError as e: # if something isn't a number
print("type in a number. ", e)

try: # add 1 to something
print(something + 1) # if it's not a number it's a TypeError
except TypeError as e: # if input isn't a number
print("type in a number. ", e)

try:
print(someting) # make a spelling mistake
except NameError as e: # if I used a wrong variable name
print("something is wrong with someting ;) ", e)

something=1000
try:
print(movies[something])
except IndexError as e: # if number is too high
print("number must be under 6 ", e)

try:
#wrap print in exec or eval so it's pre-parsed.
eval("print(something ") # missing closing parenthesis in print
except SyntaxError as e:
print("There's a bug in the code: ", e)

Answer 13

https://sololearn.com/compiler-playground/cWKRqsuDYovd/?ref=app

Answer 14

Thank you! This works. Can you explain it to a beginner?

Answer 15

Note that "eval()" and "exec()" are only for the purpose of making this demonstration work. In any other context, avoid using these functions.

Doesn't "hacking" the demo kind of defy the purpose of showing how exceptions are raised by Python?

Answer 16

Lisa
yes, it's a cheaty workaround.
but I'm out if ideas on how handle SyntaxError without crashing main...😅

at least there's no user input access to eval in the code. and the way it's written, it's guaranteed to fail, so that would somewhat minimize the security risk.

Answer 17

Thank you very much for your help. I think I'll just take it out.

Answer 18

Sorry but for what is your code Rocky Mondal?

Answer 19

Sorry to ask again. Why exactly does it not work in my script, but would work in another? Is there perhaps a better way for a syntax error that doesn't stop the whole thing immediately?

Answer 20

Jakob

you forgot the ')' in print()

line 128 should be:
⬇️ this
128 print(something) # another mistake