Python CIDR Notation to Regex Tool

cidr_to_regex.py

# CIDR Notation to Regex Tool
# Original: http://d.xenowire.net/cidr2regex.php
# Converted to Python by 112buddyd

def cidr_to_regex(cidr):
    import re
    
    # Validation
    cidr_regex = r'^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(\/([0-9]|[1-2][0-9]|3[0-2]))$'
    if not re.match(cidr_regex, cidr):
        return 'Input not valid CIDR notation. Ex. 192.168.1.0/24'
    
    # Setup Regex string dictionary
    map = {}
    # 255
    map[0] = {}
    map[0][0] = '[0-9]{1,3}'
    # 128
    map[1] = {}
    map[1][0] = '([0-9]{0,1}[0-9]|1[0-1][0-9]|12[0-7])'
    map[1][128] = '(12[8-9]|1[3-9][0-9]|2[0-5][0-9])'
    # 64
    map[2] = {}
    map[2][0] = '([0-5]{0,1}[0-9]|6[0-3])'
    map[2][64] = '(6[4-9]|[7-9][0-9]|1[0-1][0-9]|12[0-7])'
    map[2][128] = '(12[8-9]|1[3-8][0-9]|19[0-1])'
    map[2][192] = '(19[2-9]|2[0-5][0-9])'
    # 32
    map[3] = {}
    map[3][0] = '([0-2]{0,1}[0-9]|3[0-1])'
    map[3][32] = '(3[2-9]|[4-5][0-9]|6[0-3])'
    map[3][64] = '(6[4-9]|[7-8][0-9]|9[0-5])'
    map[3][96] = '(9[6-9]|1[0-1][0-9]|12[0-7])'
    map[3][128] = '(12[8-9]|1[3-5][0-9])'
    map[3][160] = '(1[6-8][0-9]|19[0-1])'
    map[3][192] = '(19[2-9]|2[0-1][0-9]|22[0-3])'
    map[3][224] = '(22[4-9]|2[3-5][0-9])'
    # 16
    map[4] = {}
    map[4][0] = '([0-9]|1[0-5])'
    map[4][16] = '(1[6-9]|2[0-9]|3[0-1])'
    map[4][32] = '(3[2-9]|4[0-7])'
    map[4][48] = '(4[8-9]|5[0-9]|6[0-3])'
    map[4][64] = '(6[4-9]|7[0-9])'
    map[4][80] = '(8[0-9]|9[0-5])'
    map[4][96] = '(9[6-9]|10[0-9]|11[0-1])'
    map[4][112] = '(11[2-9]|12[0-7])'
    map[4][128] = '(12[8-9]|13[0-9]|14[0-3])'
    map[4][144] = '(14[4-9]|15[0-9])'
    map[4][160] = '(16[0-9]|17[0-5])'
    map[4][176] = '(17[6-9]|18[0-9]|19[0-1])'
    map[4][192] = '(19[2-9]|20[0-7])'
    map[4][208] = '(20[8-9]|21[0-9]|22[0-3])'
    map[4][224] = '(22[4-9]|23[0-9])'
    map[4][240] = '2[4-5][0-9]'
    # 8
    map[5] = {}
    map[5][0] = '[0-7]'
    map[5][8] = '([8-9]|1[0-5])'
    map[5][16] = '(1[6-9]|2[0-3])'
    map[5][24] = '(2[4-9]|3[0-1])'
    map[5][32] = '3[2-9]'
    map[5][40] = '4[0-7]'
    map[5][48] = '(4[8-9]|5[0-5])'
    map[5][56] = '(5[6-9]|6[0-3])'
    map[5][64] = '(6[4-9]|7[0-1])'
    map[5][72] = '7[2-9]'
    map[5][80] = '8[0-7]'
    map[5][88] = '(8[8-9]|9[0-5])'
    map[5][96] = '(9[6-9]|10[0-3])'
    map[5][104] = '(10[4-9]|11[0-1])'
    map[5][112] = '11[2-9]'
    map[5][120] = '12[0-7]'
    map[5][128] = '(12[8-9]|13[0-5])'
    map[5][136] = '(13[6-9]|14[0-3])'
    map[5][144] = '(14[4-9]|15[0-1])'
    map[5][152] = '15[2-9]'
    map[5][160] = '16[0-7]'
    map[5][168] = '(16[8-9]|17[0-5])'
    map[5][176] = '(17[6-9]|18[0-3])'
    map[5][184] = '(18[4-9]|19[0-1])'
    map[5][192] = '19[2-9]'
    map[5][200] = '20[0-7]'
    map[5][208] = '(20[8-9]|21[0-5])'
    map[5][216] = '(21[6-9]|22[0-3])'
    map[5][224] = '(22[4-9]|23[0-1])'
    map[5][232] = '23[2-9]'
    map[5][240] = '24[0-7]'
    map[5][248] = '(24[8-9]|25[0-5])'
    # 4
    map[6] = {}
    map[6][0] = '[0-3]'
    map[6][4] = '[4-7]'
    map[6][8] = '([8-9]|1[0-1])'
    map[6][12] = '1[2-5]'
    map[6][16] = '1[6-9]'
    map[6][20] = '2[0-3]'
    map[6][24] = '2[4-7]'
    map[6][28] = '(2[8-9]|3[0-1])'
    map[6][32] = '3[2-5]'
    map[6][36] = '3[6-9]'
    map[6][40] = '4[0-3]'
    map[6][44] = '4[4-7]'
    map[6][48] = '(4[8-9]|5[0-1])'
    map[6][52] = '5[2-5]'
    map[6][56] = '5[6-9]'
    map[6][60] = '6[0-3]'
    map[6][64] = '6[4-7]'
    map[6][68] = '(6[8-9]|7[0-1])'
    map[6][72] = '7[2-5]'
    map[6][76] = '7[6-9]'
    map[6][80] = '8[0-3]'
    map[6][84] = '8[4-7]'
    map[6][88] = '(8[8-9]|9[0-1])'
    map[6][92] = '9[2-5]'
    map[6][96] = '9[6-9]'
    map[6][100] = '10[0-3]'
    map[6][104] = '10[4-7]'
    map[6][108] = '(10[8-9]|11[0-1])'
    map[6][112] = '11[2-5]'
    map[6][116] = '11[6-9]'
    map[6][120] = '12[0-3]'
    map[6][124] = '12[4-7]'
    map[6][128] = '(12[8-9]|13[0-1])'
    map[6][132] = '13[2-5]'
    map[6][136] = '13[6-9]'
    map[6][140] = '14[0-3]'
    map[6][144] = '14[4-7]'
    map[6][148] = '(14[8-9]|15[0-1])'
    map[6][152] = '15[2-5]'
    map[6][156] = '15[6-9]'
    map[6][160] = '16[0-3]'
    map[6][164] = '16[4-7]'
    map[6][168] = '(16[8-9]|17[0-1])'
    map[6][172] = '17[2-5]'
    map[6][176] = '17[6-9]'
    map[6][180] = '18[0-3]'
    map[6][184] = '18[4-7]'
    map[6][188] = '(18[8-9]|19[0-1])'
    map[6][192] = '19[2-5]'
    map[6][196] = '19[6-9]'
    map[6][200] = '20[0-3]'
    map[6][204] = '20[4-7]'
    map[6][208] = '(20[8-9]|21[0-1])'
    map[6][212] = '21[2-5]'
    map[6][216] = '21[6-9]'
    map[6][220] = '22[0-3]'
    map[6][224] = '22[4-7]'
    map[6][228] = '(22[8-9]|23[0-1])'
    map[6][232] = '23[2-5]'
    map[6][236] = '23[6-9]'
    map[6][240] = '24[0-3]'
    map[6][244] = '24[4-7]'
    map[6][248] = '(24[8-9]|25[0-1])'
    map[6][252] = '25[2-5]'
    
    # Setup some vars
    network = cidr.split('/')[0]
    n1 = network.split('.')[0]
    n2 = network.split('.')[1]
    n3 = network.split('.')[2]
    n4 = network.split('.')[3]
    mask = cidr.split('/')[1]
    bip = 0
    
    # Logic based on subnet mask
    if mask == '0':
        return map[0][0] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '1':
        bip = int((int(n1)/128)*128)
        map[1][bip] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '2':
        bip = int((int(n1)/64)*64)
        return map[2][bip] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '3':
        bip = int((int(n1)/32)*32)
        return map[3][bip] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '4':
        bip = int((int(n1)/16)*16)
        return map[4][bip] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '5':
        bip = int((int(n1)/8)*8)
        return map[5][bip] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '6':
        bip = int((int(n1)/4)*4)
        return map[6][bip] + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '7':
        bip = int((int(n1)/2)*2)
        if len(str(bip)) == 2:
            return str(bip)[0] + '[' + str(bip)[1] + '-' + str(bip+1)[1] + ']' + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
        elif len(str(bip)) == 3:
            return str(bip)[:2] + '[' + str(bip)[2] + '-' + str(bip+1)[2] + ']' + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
        else:
            return '[' + str(bip) + '-' + str(bip+1) + ']' + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
        
    elif mask == '8':
        return n1 + '\.' + map[0][0] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '9':
        bip = int((int(n2)/128)*128)
        return n1 + '\.' + map[1][bip] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '10':
        bip = int((int(n2)/64)*64)
        return n1 + '\.' + map[2][bip] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '11':
        bip = int((int(n2)/32)*32)
        return n1 + '\.' + map[3][bip] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '12':
        bip = int((int(n2)/16)*16)
        return n1 + '\.' + map[4][bip] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '13':
        bip = int((int(n2)/8)*8)
        return n1 + '\.' + map[5][bip] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '14':
        bip = int((int(n2)/4)*4)
        return n1 + '\.' + map[6][bip] + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '15':
        bip = int((int(n2)/2)*2)
        if len(str(bip)) == 2:
            return n1 + '\.' + str(bip)[0] + '[' + str(bip)[1] + '-' + str(bip+1)[1] + ']' + '\.' + map[0][0] + '\.' + map[0][0]
        elif len(str(bip)) == 3:
            return n1 + '\.' + str(bip)[:2] + '[' + str(bip)[2] + '-' + str(bip+1)[2] + ']' + '\.' + map[0][0] + '\.' + map[0][0]
        else:
            return n1 + '\.' + '[' + str(bip) + '-' + str(bip+1) + ']' + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '16':
        return n1 + '\.' + n2 + '\.' + map[0][0] + '\.' + map[0][0]
    elif mask == '17':
        bip = int((int(n3)/128)*128)
        return n1 + '\.' + n2 + '\.' + map[1][bip] + '\.' + map[0][0]
    elif mask == '18':
        bip = int((int(n3)/64)*64)
        return n1 + '\.' + n2 + '\.' + map[2][bip] + '\.' + map[0][0]
    elif mask == '19':
        bip = int((int(n3)/32)*32)
        return n1 + '\.' + n2 + '\.' + map[3][bip] + '\.' + map[0][0]
    elif mask == '20':
        bip = int((int(n3)/16)*16)
        return n1 + '\.' + n2 + '\.' + map[4][bip] + '\.' + map[0][0]
    elif mask == '21':
        bip = int((int(n3)/8)*8)
        return n1 + '\.' + n2 + '\.' + map[5][bip] + '\.' + map[0][0]
    elif mask == '22':
        bip = int((int(n3)/4)*4)
        return n1 + '\.' + n2 + '\.' + map[6][bip] + '\.' + map[0][0]
    elif mask == '23':
        bip = int((int(n3)/2)*2)
        if len(str(bip)) == 2:
            return n1 + '\.' + n2 + '\.' + str(bip)[0] + '[' + str(bip)[1] + '-' + str(bip+1)[1] + ']' + '\.' + map[0][0]
        elif len(str(bip)) == 3:
            return n1 + '\.' + n2 + '\.' + str(bip)[:2] + '[' + str(bip)[2] + '-' + str(bip+1)[2] + ']' + '\.' + map[0][0]
        else:
            return n1 + '\.' + n2 + '\.' + '[' + str(bip) + '-' + str(bip+1) + ']' + '\.' + map[0][0]
    elif mask == '24':
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[0][0]
    elif mask == '25':
        bip = int((int(n4)/128)*128)
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[1][bip]
    elif mask == '26':
        bip = int((int(n4)/64)*64)
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[2][bip]
    elif mask == '27':
        bip = int((int(n4)/32)*32)
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[3][bip]
    elif mask == '28':
        bip = int((int(n4)/16)*16)
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[4][bip]
    elif mask == '29':
        bip = int((int(n4)/8)*8)
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[5][bip]
    elif mask == '30':
        bip = int((int(n4)/4)*4)
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + map[6][bip]
    elif mask == '31':
        bip = int((int(n4)/2)*2)
        if len(str(bip)) == 2:
            return n1 + '\.' + n2 + '\.' + n3 + '\.' + str(bip)[0] + '[' + str(bip)[1] + '-' + [string](bip+1)[1] + ']'
        elif len(str(bip)) == 3:
            return n1 + '\.' + n2 + '\.' + n3 + '\.' + str(bip)[:2] + '[' + str(bip)[2] + '-' + [string](bip+1)[2] + ']'
        else:
            return n1 + '\.' + n2 + '\.' + n3 + '\.' + '[' + str(bip) + '-' + str(bip+1) + ']'
    elif mask == '32':
        return n1 + '\.' + n2 + '\.' + n3 + '\.' + n4
    else:
        return 'Invalid Subnet Mask.'
        
        
if __name__ == '__main__':
    print('RegEx: ' + cidr_to_regex(input('CIDR:  ')))

You have a minor bug here:
Instead of:

    n1 = cidr.split('.')[0]
    n2 = cidr.split('.')[1]
    n3 = cidr.split('.')[2]
    n4 = cidr.split('.')[3]

It should be:

    n1 = network.split('.')[0]
    n2 = network.split('.')[1]
    n3 = network.split('.')[2]
    n4 = network.split('.')[3]

Otherwise it raises an error with n4 (it captures the slash and mask as well)

Nice find, got it fixed. Thanks!

Line 275 and 277 you have an undefined variable named string

What is it supposed to be ?

My guess would to replace [string] with str

My guess would to replace [string] with str

[string](bip+1)[2] -> str(bip+1)[2] will not work either.

After replacing [string] with str (as in having str(bip+1)[2] in line 283) works great for me, except for a bug in line 279 (which seems like a recurring bug in all of the bip = int((int(n4) / X) * X) that gets the last bit wrong. It should be bip = int((int(n4) / X)) * X (X being a different power of 2 in every instance).

Once I changed [string] to str and line 279 to bip = int((int(n4) / 2)) * 2, I got the same results for my CIDR as this website gave me: https://www.ipaddressguide.com/cidr.

@Raznak - do you have an example for which it doesn't work after those changes?

@ewino Well seen. This should do it :)