What is an example of try/except?

In the lesson, we are taught that “try” and “except” statements are used to check for possible errors a user might encounter. However, I suppose that the process of checking errors does not fulfill the final scope of any control flow, but it is just used complementary in order to write a clean code without errors.
If this right, I would expect that “try” and “except” statements would be used in conjuction with other statements such as “if, else” etc, all written in the same code/function.
So, my question is , which is the right order to combine all these statements when writing the parts of a function? Could you please give an example?

the vital piece of information missing here is that we can also throw exceptions:

def validate_username(username):
    if ( len(username) < 5 ):
        raise Exception("Username to short")
def main():
    username = raw_input("input username: ") # replace with input if you use python3
    except Exception as e:

this also explains what happens when exceptions occur.

you could expand the validate_username() function with a lot more exceptions, so then the control flow logic (if, elif, else) is within the validate_username, then other people can use your function handle the exception as they like.


def raises_value_error():
raise ValueError

except ValueError:
print(“You raised a ValueError!”)

Do we need indent "try"and “except”? If they are statements like “if” in a function, why is the indention different ?

try and except have the same nesting rules? When you want a try/except statement within an if statement you get:

if some_condition:
        # some code
    except SomeException:
        # something to do when the exception occured

I do not see any result on console for my code. Please help me to know where I made a mistake.

Your indention/nesting is off. print(shipping_cost_drone(1.5)) is nested in the body of the function itself, and unreachable after a return statement, just to name one thing.

Okay, so can we use if-else control flow inside a try statement to check for different errors? I know it may be a lengthier process and a longer code, but just out of curiosity…

I am referring to the process of checking multiple errors as illustrated by @jephos249 on this page:

you could, but the recommend way would be what appylpye does:

# Slice the pizza!
pizza_mass = 320.0 # 320.0 grams
while True:
    num_slices = int(input("Serve the pizza as how many slices? "))
    slice_mass = pizza_mass / num_slices
  except ValueError: # Input cannot be interpreted as an int.
    print("Enter an integer, please.")
  except ZeroDivisionError: # Input was 0.
    print("Cannot serve it as zero slices.")
  if num_slices < 0: # Input was negative.
    print("Cannot serve a negative number of slices.")

print("The mass of each pizza slice is {:0.2f} grams.".format(slice_mass))

to use multiple except clauses.


Great! That helped a lot… Thank you Sir !!!

In the try can i use more than one variable like
nikola_tesla, richard_p_feyman
except (valueError, SyntaxError,…)
print(“I don’t know”)

The try block can contain the code we would normally use as if there were no errors expected. The variables are not a factor. It’s just code that may raise an exception, hence the try block and its attendant except to handle the exceptions.

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Understood my professor. Thank you.

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