Velocity Reviews > str to float (rounded)

# str to float (rounded)

Guest
Posts: n/a

 06-10-2008
Hello,

I have a list of tuple with strin elements. These elements are number,
but they are save as string. Now I will change the string to number
which will be rounded. An example will make it more clear.

t = [('35.757', '-0.239'), ('33.332', '-2.707'), ('33.640', '-2.423')]

And I will have the next list:

t = [(35.76, -2.24), (33.33, -2.71), (33.64, -2.42)]

The elements of tuple are not more as string.

Would somebody tell me how I can do that?

Regards,

Diez B. Roggisch
Guest
Posts: n/a

 06-10-2008

> Hello,
>
> I have a list of tuple with strin elements. These elements are number,
> but they are save as string. Now I will change the string to number
> which will be rounded. An example will make it more clear.
>
> t = [('35.757', '-0.239'), ('33.332', '-2.707'), ('33.640', '-2.423')]
>
> And I will have the next list:
>
> t = [(35.76, -2.24), (33.33, -2.71), (33.64, -2.42)]
>
> The elements of tuple are not more as string.
>
> Would somebody tell me how I can do that?

use

float("123.45")

to convert a string to a float.

Of course you need to do that on all your elements above by e.g. a
list-comprehension.

Diez

Guest
Posts: n/a

 06-10-2008
On Jun 10, 4:30 pm, "Diez B. Roggisch" <(E-Mail Removed)> wrote:
> > Hello,

>
> > I have a list of tuple with strin elements. These elements are number,
> > but they are save as string. Now I will change the string to number
> > which will be rounded. An example will make it more clear.

>
> > t = [('35.757', '-0.239'), ('33.332', '-2.707'), ('33.640', '-2.423')]

>
> > And I will have the next list:

>
> > t = [(35.76, -2.24), (33.33, -2.71), (33.64, -2.42)]

>
> > The elements of tuple are not more as string.

>
> > Would somebody tell me how I can do that?

>
> use
>
> float("123.45")
>
> to convert a string to a float.
>
> Of course you need to do that on all your elements above by e.g. a
> list-comprehension.
>
> Diez

If I do the next :

t1 = [(round(float(x),1), round(float(y),2)) for x, y in t]

I get the long float as :

[(35.799999999999997, -0.23999999999999999), (33.299999999999997,
-2.71), (33.600000000000001,-2.4199999999999999)]

But I would have a float with 2 decimal numbers.

Diez B. Roggisch
Guest
Posts: n/a

 06-10-2008
>
> If I do the next :
>
> t1 = [(round(float(x),1), round(float(y),2)) for x, y in t]
>
> I get the long float as :
>
> [(35.799999999999997, -0.23999999999999999), (33.299999999999997,
> -2.71), (33.600000000000001,-2.4199999999999999)]
>
> But I would have a float with 2 decimal numbers.

There is no such thing as a float with only two decimal numbers. This has
been discussed on this ML a bazillion times - what you see above are
rounding errors due to the approximation of decimal values by binary
floating points.

You can *convert a float to a string* and specify a precision when printing:

>>> print "%.2f" % 2.4199999999999999999999999

2.42

Or you can use the module decimal to work with numbers base 10 - which you
can also limit to certain precisions. See a recent thread on this ML,
google for "Alternative to decimal type"

Diez