Using regex to add leading zeroes

Question

I would like to add a certain number of leading zeroes (say up to 3) to all numbers of a string. For example:

Input: /2009/5/song 01 of 12

Outpu

Answer 1

Combined in Xcode:

targetName=[NSString stringWithFormat:@"%05d",number];

Gives 00123 for number 123

Answer 2

Another approach:

>>> x
'/2009/5/song 01 of 12'
>>> ''.join([i.isdigit() and i.zfill(4) or i for i in re.split("(?<!\d)(\d+)(?!\d)",x)])
'/2009/0005/song 0001 of 0012'
>>>

Or:

>>> x
'/2009/5/song 01 of 12'
>>> r=re.split("(?<!\d)(\d+)(?!\d)",x)
>>> ''.join(a+b.zfill(4) for a,b in zip(r[::2],r[1::2]))
'/2009/0005/song 0001 of 0012'

Answer 3

Use something that supports a callback so you can process the match:

>>> r=re.compile(r'(?:^|(?<=[^0-9]))([0-9]{1,3})(?=$|[^0-9])')
>>> r.sub(lambda x: '%04d' % (int(x.group(1)),), 'dfbg345gf345', sys.maxint)
'dfbg0345gf0345'
>>> r.sub(lambda x: '%04d' % (int(x.group(1)),), '1x11x111x', sys.maxint)
'0001x0011x0111x'
>>> r.sub(lambda x: '%04d' % (int(x.group(1)),), 'x1x11x111x', sys.maxint)
'x0001x0011x0111x'

Answer 4

C# version

        string input = "/2009/5/song 01 of 12";
        string regExPattern = @"(\/\d{4}\/)(\d+)(\/song\s+)(\d+)(\s+of\s+)(\d+)";
        string output = Regex.Replace(input, regExPattern, callback =>
        {
            string yearPrefix = callback.Groups[1].Value;
            string digit1 = int.Parse(callback.Groups[2].Value).ToString("0000");
            string songText = callback.Groups[3].Value;
            string digit2 = int.Parse(callback.Groups[4].Value).ToString("0000");
            string ofText = callback.Groups[5].Value;
            string digit3 = int.Parse(callback.Groups[6].Value).ToString("0000");
            return $"{yearPrefix}{digit1}{songText}{digit2}{ofText}{digit3}";
        });

Answer 5

Using c#:

string result = Regex.Replace(input, @"\d+", me =>
{
    return int.Parse(me.Value).ToString("0000");
});