base converter

[Alex Martelli]

"Greg Jorgensen" <gregj at pobox.com> wrote in message
news:GE_V6.166783$p33.3516294 at news1.sttls1.wa.home.com...
>
> "Fredrik Lundh" <fredrik at pythonware.com> wrote:
>
> > def BaseConvert(x, b):
> >     out = ""
> >     while x:
> >         x, d = divmod(x, b)
> >         out = str(d) + out
> >     return out
> >
>
> Slightly modified to work with bases > 10:
>
> def BaseConvert(x, b):
>     "convert decimal number x to base b"
>     digits = "0123456789ABCDEF"
>     out = ""
>     if b <= len(digits):
>         while x:
>             x, d = divmod(x, b)
>             out = digits[d] + out
>     return out

In general, I think it's better to avoid building a
string by a loop concatenating single characters.  It
may not matter much in this case, but...

def BaseConvert(x, b):
    import string
    digits = string.digits + string.uppercase
    if b>len(digits):
        raise ValueError, "base %s too large"%b
    if x == 0:
        return '0'
    elif x<0:
        negative = 1
        x = -x
    else:
        negative = 0
    result = []
    while x:
        x, d = divmod(x, b)
        result.append(digits[d])
    if negative:
        result.append('-')
    result.reverse()
    return ''.join(result)

I've also tried to fix the bug which (I believe)
would make this loop endlessly for x<0, &c.


Alex