[Tutor] Out of range

[Magnus Lycka]

At 09:49 2003-02-05 -03-30, Adam Vardy wrote:
>Which conversions were they?

Two functions called sci2float and float2sci.

>If I sort just some plain numbers, I am
>still left with some unsorted lines of text.

 >>> i = 5
 >>> type(i)
<type 'int'>
 >>> s = '5'
 >>> type(s)
<type 'str'>

Just because a string only contains digits doesn't mean that
it becomes a number in Python. Some languages behave in that
way, and it can cause a lot of problems. In python you must
explicitly tell the computer to extract a number from a string
if you want that.

 >>> s = '5'
 >>> i = int(s)
 >>> print i, type(i)
5 <type 'int'>
 >>> f = float(s)
 >>> print f, type(f)
5.0 <type 'float'>

In a few selected cases, Python will actually perform an implicit
type conversion. For instance, you don't have to do

a = 5
b = 6.3
print float(a) + b

Python will automatically coerce a float and an integer on addition,
so you can just type

a = 5
b = 6.3
print a + b

and get the float 11.3 as result, but you can never do

print 5 + '6.3'

Python will refuse to convert strings to numbers implicitly.

In some languages, OCaml for instance, you must explicitly convert
an integer to a float if you want to add it to another float. This
is partly a tradeoff between convenience and performance. It's also
an issue of avoiding bugs. I think Python strikes the right balance.


-- 
Magnus Lycka, Thinkware AB
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