[Tutor] dealing with user input whose value I don't know

[David]

Cheers for the insights!

However, I just found out that changing input() to raw_input() breaks my 
code:

This program takes the average of numbers you supply!!
How many numbers do you want me to work with? 2
You want me to take the average of 2 numbers.
Please type the numbers, separated by commas: 1,2
You want to know the average of the numbers: 1,2
Traceback (most recent call last):
  File "avgInput.py", line 13, in <module>
    add = add + i
TypeError: unsupported operand type(s) for +: 'int' and 'str'

**** End of process output ****

The reason being, I take, that

numbers = raw_input("Please type the numbers, separated by commas: ")

also returns the comma (1,2) and thus the for loop can't cope...
So should I therefore retain

numbers = input("Please type the numbers, separated by commas: ") ?

Otherwise I don't know (yet) what to do....

David


Bill Campbell wrote:
> On Thu, Oct 02, 2008, Steve Willoughby wrote:
>   
>> On Fri, Oct 03, 2008 at 01:38:48AM +0800, David wrote:
>>     
>>> Does that mean input() is obsolete (after all, Zelle's book is not the 
>>> freshest on the shelf)? Or do they have different uses?
>>>       
>> Depends on how you look at it.
>>
>> input() automatically evaluates whatever the user types as a Python
>> expression and returns the result.  So if they type 5, the integer
>> 5 is returned.  For your program, that's probably what you want, and
>> has the advantage of letting you type something like 2+3 so your user
>> can let Python evaluate math expressions.
>>
>> On the other hand, you'd think that you could ask a user for a text
>> response using input():
>>   name = input("What is your name? ")
>>   print "Hello, ", name
>>
>> But if they just type the answer, Python will crash with an error
>> because it's expecting a legal Python expression there (so a 
>> string value would have to be typed in quotes).
>>     
>
> Remember the cardinal rule NEVER TRUST USER INPUT!  Always check
> for validity, and use methods that prevent malicious strings from
> allowing the user to get unauthorized access or change things
> they shouldn't.
>
> Many of the common exploits of web pages are the result of poor
> checking of input resulting in sql injection attacks, and other
> breaches.
>
> Bill
>