[Tutor] ValueError

[Johnson Tran]

I am using python 2.5...and adding raw_input has fixed the issue, thank you!

On May 3, 2011, at 5:01 AM, Peter Otten wrote:

> Johnson Tran wrote:
> 
>> Thanks for the replies..so I added the "try" block but it still does not
>> seem to be outputting my default error message:
>> 
>> def Conversion():
>>    try:
>> 
>>        print "This program converts the first value from inches to
>>        centimeters and second value centimeters to inches." print "(1
>>        inch = 2.54 centimeters)" inches = input("Enter length in inches:
>>        ") centimeters = 2.54 * float(inches)
>>        print "That is", centimeters, "centimeters."
>>        centimeters = input("Enter length in centimeters: ")
>>        inch = float(centimeters) / 2.54
>>        print "That is", inch, "inches."
>> 
>>    except ValueError:
>>         print "Invalid digit, please try again."
>> Conversion()
>> 
>> Error message:
>> 
>> Traceback (most recent call last):
>>  File "/Users/JT/Desktop/hw#2.py", line 16, in <module>
>>    Conversion()
>>  File "/Users/JT/Desktop/hw#2.py", line 9, in Conversion
>>    centimeters = input("Enter length in centimeters: ")
>>  File "<string>", line 1, in <module>
>> NameError: name 'fs' is not defined
> 
> input() in Python 2.x tries to evaluate your input as a Python expression, 
> so if you enter "2*2" it gives you 4, and when you enter "fs" it tries to 
> look up the value of a global variable "fs" in your python script. You don't 
> have such a variable in your script, so it complains with a NameError.
> 
> The best way to avoid such puzzling behaviour is to use raw_input() instead 
> of input().
> 
> Also you should make the try...except as narrow as possible
> 
> try:
>    centimeters = float(centimeters)
> except ValueError as e:
>    print e
> 
> is likely to catch the float conversion while with many statements in the 
> try-suite you are more likely to hide a problem that is unrelated to that 
> conversion.
> 
> PS: In Python 3.x raw_input() is gone, but input() behaves like raw_input() 
> in 2.x
> 
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