Payal: > -----Original Message----- > Date: Mon, 17 Apr 2006 13:24:31 -0400 > From: Payal Rathod <[EMAIL PROTECTED]> > Subject: Re: [Tutor] functions in Python > To: Steve Nelson <[EMAIL PROTECTED]> > Cc: "Python\[Tutor\]" <tutor@python.org> > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=us-ascii > > On Mon, Apr 17, 2006 at 05:42:05PM +0100, Steve Nelson wrote: > > When you define a function, you are writing a block of code which you > > can ask to perform a task. The task may be simple, and not require > > any additional information, or it may be more complex and need > > information. > > What is the difference between, > > >>> def f(x): > ... return x > ... > >>> f(4) > 4 > > >>> def f(x): > ... print x > ... > >>> f(4) > 4 > > Both give same results. So, why return statement is needed? > With warm regards, > -Payal
Let's use your two functions named and see what we can do with them. In order to use both function definitions in the same interactive session, I will name the first 'f1' and the second 'f2'. >>>>>>>>>> >>> def f1(x): ... return x ... >>> def f2(x): ... print x ... >>>>>>>>>> Okay so far? Now, let's use each of these functions in a simple computation. To start, we'll just add two integers (called literals in programming jargon), >>>>>>>>>> >>> 4 + 4 8 >>>>>>>>>> The '+' operator takes two integers, adds them together and gives back (returns) the result. (Actually, the '+' operator can do more than this, but this is enough for this example.) Now, we'll do the same calculation using f1 instead of the literals. >>>>>>>>>> >>> f1(4) + f1(4) 8 >>>>>>>>>> This worked as expected: f1 sent back (returned) the value we gave it (the argument 4) and the '+' operator did the addition. Questions? Now, let's do the same calcuation once more, using f2 this time. >>>>>>>>>> >>> f2(4) + f2(4) 4 4 Traceback (most recent call last): File "<input>", line 1, in ? TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType' >>>>>>>>>> This time the operation failed. The f2 function did what we wrote it to do: it printed the argument to the Standard Output device (also called STDOUT), the interactive shell window in this case. But, as the error message indicates, it also RETURNED a value: in this case None, which has the type NoneType. The '+' operator then tried to add the two None values together and failed. The examples above show that, although the output of f1 and f2 look the same, it is actually different. The 'f2' function displays its argument for humans to read. The 'f1' function makes the argument available for other code to use. That is the purpose of the 'return' statement: to make the results of the function available to other code. It is important to remember that, in Python, EVERY function returns a value. If a 'return' statement is included in the function, the value the result of the expression associated with the statement (in your example, 4). If no 'return' statement is included, the function returns None. I hope this makes sense to you. If not, keep asking questions. Best Regards, Barry [EMAIL PROTECTED] 541-302-1107 ________________________ We who cut mere stones must always be envisioning cathedrals. -Quarry worker's creed _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
