random guy - 1 year ago 133
Python Question

# Python elegant inverse function of int(string,base)

python allows conversions from string to integer using any base in the range [2,36] using:

``````int(string,base)
``````

im looking for an elegant inverse function that takes an integer and a base and returns a string

for example

``````>>> str_base(224,15)
'ee'
``````

i have the following solution:

``````def digit_to_char(digit):
if digit < 10: return chr(ord('0') + digit)
else: return chr(ord('a') + digit - 10)

def str_base(number,base):
if number < 0:
return '-' + str_base(-number,base)
else:
(d,m) = divmod(number,base)
if d:
return str_base(d,base) + digit_to_char(m)
else:
return digit_to_char(m)
``````

note: digit_to_char() works for bases <= 169 arbitrarily using ascii characters after 'z' as digits for bases above 36

is there a python builtin, library function, or a more elegant inverse function of int(string,base) ?

This thread has some example implementations.

Actually I think your solution looks rather nice, it's even recursive which is somehow pleasing here.

I'd still simplify it to remove the `else`, but that's probably a personal style thing. I think `if foo: return` is very clear, and doesn't need an `else` after it to make it clear it's a separate branch.

``````def digit_to_char(digit):
if digit < 10:
return str(digit)
return chr(ord('a') + digit - 10)

def str_base(number,base):
if number < 0:
return '-' + str_base(-number, base)
(d, m) = divmod(number, base)
if d > 0:
return str_base(d, base) + digit_to_char(m)
return digit_to_char(m)
``````

I simplified the 0-9 case in `digit_to_char()`, I think `str()` is clearer than the `chr(ord())` construct. To maximize the symmetry with the `>= 10` case an `ord()` could be factored out, but I didn't bother since it would add a line and brevity felt better. :)

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download