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Control Flow
Try and Except Statements

if, elif, and else statements aren’t the only way to build a control flow into your program. You can use try and except statements to check for possible errors that a user might encounter.

The general syntax of a try and except statement is

try: # some statement except ErrorName: # some statement

First, the statement under try will be executed. If at some point an exception is raised during this execution, such as a NameError or a ValueError and that exception matches the keyword in the except statement, then the try statement will terminate and the except statement will execute.

Let’s take a look at this in an application. I want to write a function that takes two numbers, a and b as an input and then returns a divided by b. But, there is a possibility that b is zero, which will cause an error, so I want to include a try and except flow to catch this error.

def divides(a,b): try: result = a / b print (result) except ZeroDivisionError: print ("Can't divide by zero!")

Now that you see how it works, try to write one yourself.



The function in the editor is very simple and serves one purpose: it raises a ValueError.

Try running it by entering raises_value_error() into the code editor and hitting run.

Remember, unindent this function call so it isn’t included in the function itself.


Great! Nice error raising! Now let’s make that error message a little more palatable.

Write a try statement and an except statement around the line of code that executes the function to catch a ValueError and make the error message print You raised a ValueError!

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