Get the string in 2 digit format with leading zeros in python

Question

I have a requirement to add 2 string which are in mac format as hex which has 9 octets. As part of that I have achieved almost, but one final thing pending is to get the value in 2 digit format.

string1= "aa.aa.aa.aa.aa.aa.aa.aa.ff"
string2= "00.00.00.00.00.00.00.00.01"

when I add these 2 the out put I get is aa.aa.aa.aa.aa.aa.aa.ab.0 but I want value to be aa.aa.aa.aa.aa.aa.aa.ab.00 . (2 zeros).

I tried using

temp = '%02d' % string3

but I got error

TypeError: %d format: a number is required, not str

as I am trying to do that with string.

Avinash I am adding two string in Hex format so ff+1 will be 1 00 with 1 carry backwards so here aa.ff becomes ab.00 — Ravi Kiran, Aug 02 '15 at 14:25

score 1 · Answer 1 · edited May 23 '17 at 12:21

1

You can split the string, pad each part with leading zeros and join it again:

s = "aa.aa.aa.aa.aa.aa.aa.ab.0"
print '.'.join(["{0:0>2}".format(w) for w in s.split('.')])

Output:

aa.aa.aa.aa.aa.aa.aa.ab.00

(The padding is based on this answer.)

Even shorter version based on map:

print '.'.join(map("{0:0>2}".format, s.split('.')))

edited May 23 '17 at 12:21

Community

1
1

answered Aug 02 '15 at 08:20

Falko

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Thank you so much Falko. It worked. Which one is better among both methods? Padding or map based? – Ravi Kiran Aug 02 '15 at 08:31
The `format` function does the padding. So the difference is using a [list comprehension](http://www.secnetix.de/olli/Python/list_comprehensions.hawk) or the `map` function. In my point of view it doesn't really matter which one to use here. With `map` you save a temporary variable, which might improve readability. – Falko Aug 02 '15 at 08:33

score 0 · Answer 2 · edited May 23 '17 at 11:58

Instead of fixing the resulting string3, you can improve the way you create it. If you convert the summands to integers, add them and convert the result back to a hex representation, you don't have to worry about missing zeros:

a = "aa.aa.aa.aa.aa.aa.aa.aa.ff"
b = "00.00.00.00.00.00.00.00.01"
c = hex(int(a.replace('.', ''), 16) + int(b.replace('.', ''), 16))[2:-1]
print '.'.join(i+j for i,j in zip(c[::2], c[1::2]))

Output:

aa.aa.aa.aa.aa.aa.aa.ab.00

References:

Converting hex to int: https://stackoverflow.com/a/209550/3419103
Converting int to hex: https://stackoverflow.com/a/2269836/3419103
Inserting a . every two characters: https://stackoverflow.com/a/3258596/3419103

This is awesome. I have around 15 lines of code to do this. but you made in just 3 lines...Genius. Thanks again. — Ravi Kiran, Aug 02 '15 at 08:36

Get the string in 2 digit format with leading zeros in python

2 Answers2