Problems with conversion of values in strings to integers

[Jørgen Cederberg]

Bengt Richter wrote:

> On Mon, 06 Oct 2003 14:06:26 +0200, Peter Otten <__peter__ at web.de> wrote:
> 
>>Jørgen Cederberg wrote:
>>
>>> Hi,
>>> 
>>> using Python 2.2.1 on Windows and QNX I'm having trouble understandig
>>> why int() raises a ValueError exception upon converting strings.
>>> 
<snip example of converting strings/floats with int()>
>>> 
>>> This is quite frustating. The only solution I can see is to do:
>>>  >>> int(float('10.1'))
>>> 10
>>> 
>>> Is this the only solution or are there any other way to do this?
>>
>>
<snip - atoi example>
>>
>>>>> int(float("1.999"))
>>1
>>
>>>>> int(round(float("1.999")))
>>2
>>
>>I think it's good that Python does not make the decision for you. Once you
>>have decided which route to go you can easily wrap it into a helper
>>function, e. g.
>>
>>def toInt(s):
>>    try:
>>        return int(s)
>>    except ValueError:
>>        return int(round(float(s)))
>>
>>(When dealing with user input, things are a little more complicated, as the
>>decimal separator changes between locales)
>>
> There's that too ;-)

Actually my problem arose using the Scale widget in Tkinter. The small 
program below demonstrates the problem.

The first line with Scale doesn't work, as the IntVar(!), tries to 
convert a string from Tkinter, that is in fact a float. This results 
from the Tkinter function getint, which is the same as int.

--------------------------
from Tkinter import *

def onScale(value):
     print "The value is", value,"and its type is", type(value)
     print "The variable is", var.get(),"and its type is", type(var.get())

root = Tk()
var = IntVar()

# This does'nt work. The value inside the Scale is now a float 
represented in
# string, which int() can't handle.
#s = Scale(root, length=100, bd=1, digit=3, from_ = -10, 
#to=10,variable=var, command=onScale)

# This works.
s = Scale(root, length=100, bd=1, from_ = -10, to=10,variable=var, 
command=onScale)
s.pack()

root.mainloop()
--------------------------

One might argue that it doesn't make sense to use the Scale with digits 
together with an IntVar, but in my case to from_ and to values can both 
be integers and floats.

Regards
Jorgen