# [Tutor] Can't figure out syntax error

Kent Johnson kent37 at tds.net
Fri Jun 10 04:29:55 CEST 2005

```as.20.schellenberg at spamgourmet.com wrote:
> Hi there,
>
> I'm in the process of learning Python, and need some help deciphering
> the reason why the following code doesn't work:

>
> import sys, string
>
> def dec2bin(decNum):
> 	# validate the input as a postive integer number
> 	for char in decNum:
> 		if str(char).isdigit() == False:

char is already a string so you don't have to call str(char), just use char directly:
if char.isdigit() == False:

but you don't have to compare to False, either, just say
if not char.isdigit():

in fact you can call isdigit() on the whole string, it will test if all the characters are digits. So instead of the loop just write
if not decNum.isdigit():

> 			print "Not a postive integer number given when calling the dec2bin
> function."
> 			sys.exit()
>
> 	bin = ""					# initialize the new binary result (as a string)
> 	num = int(decNum)

OK, num is an integer now.
>
> 	if num == 0:				# take care of the zero case
> 		bin = "0"
>
> 	while int(num) != 0:				# the rest of the cases
> 		nextBin = int(num) % 2		# check if this column should be a 0 or 1
> 		bin = str(nextBin) + bin		# add the result to the front of the result
> string
> 		int(num) = int(num) / 2		# this is integer division, so we truncate
> the decimal part

You don't have to keep saying int(num), num is already an int and dividing by 2 gives a new int. You can just use num directly.
>
> 	return bin						# return the binary result
>
> # testing
> x = "13"
> print dec2bin(x)

Kent

```