Using return With try and finally Blocks

00:00 In Python, when you write code that you know may cause an exception, you typically use it with a try statement. One of the features of a try statement is an optional finally clause, which is executed whether or not there was actually an exception.

00:15 Real Python has an introduction to exceptions tutorial, where you can read more information about the try statement. In this lesson, we’ll be looking specifically at using the return statement and try statements that have a finally clause.

00:32 Simply put, when you use a return statement inside a try statement that has a finally clause, that finally clause is always executed before the return statement. Specifically, this means that the finally clause will always be executed when the try statement is encountered.

00:52 So even though the finally clause may appear after one or more return statements, it should not be viewed as dead code. Here is an example of a try statement.

01:04 This function takes a parameter, value, and attempts to convert it to a floating-point value. If successful, that floating-point value will be returned.

01:14 If not, a string will be returned. But before returning, the print statement and the finally clause will be executed.

01:24 Here’s that same function with a single parameter, value. The function will attempt to convert the argument provided for value into a floating-point value.

01:38 If that argument is not something that represents a floating-point value, then the call to float() will cause an error, so this function call is placed in a try statement.

01:50 If the statement is successful, then the floating-point value it represents will be returned. If it is unsuccessful, then a ValueError will occur, and the return statement in the except clause will be executed, which returns the argument in values as a string.

02:13 In either case, since this try statement has a finally clause, it will be executed before the function returns. So for any argument in value, we will see the phrase Run this before returning printed before the function ends. And in an interactive session, we’ll see the return value after that print statement.

02:38 So if I try to run this, we will see the print statement for any argument provided to the function and then the appropriate return value is returned to the calling environment.

02:48 Let’s check this out. We’ll import this function.

02:55 Let’s first try this out with an argument for which the float() function will succeed.

03:02 We can see the integer 9 was converted to the floating-point value 9.0 and returned, but this was displayed after the message Run this before returning.

03:14 Here’s one where it will fail.

03:19 First, we see the Run this before returning message, and here, 'one' was returned as a string. We hit the except part of this try statement.

03:35 So remember that any code that is in a finally clause will always be executed before any return statements in either the try or except clauses. In your last lesson, we will look at using the return statement in generator functions.