[Level 2] Implement prefix and netmask transfer with Python.

Sometimes, you want to transfer between netmask and prefix setting.
You can use the following sample script which is written by Python.
#!/bin/env python
def transferPrefix2Netmask(self, prefix):
        netmask = ''
        nLeadingFF = prefix / 8
        netmask += '.'.join(['255']*nLeadingFF)
        if nLeadingFF != 4:
            netmask += '.' + str(256-2**(8-prefix%8))
        nSuffix00 = 3 - nLeadingFF
        if nLeadingFF < 3:
            netmask += '.' + '.'.join(['00']*nSuffix00)
        return netmask
    
    def transferNetmask2Prefix(self, netmask):
        prefix = 0
        left = 0
        for i in netmask.split('.'):
            if i == '255':
                prefix += 8
            else:
                left = int(i)
                break
        if left != 0:
            for n in range(7, 0, -1):
                prefix += 1
                if left - 2 ** n == 0:
                    break
                else:
                    left -= 2 ** n
        return prefix

print transferPrefix2Netmask(16)
print transferPrefix2Netmask(17)
print transferPrefix2Netmask(18)
print transferPrefix2Netmask(22)
print transferPrefix2Netmask(23)
print transferPrefix2Netmask(24)
print transferNetmask2Prefix('255.255.128.0')
print transferNetmask2Prefix('255.255.192.0')
print transferNetmask2Prefix('255.255.252.0')
print transferNetmask2Prefix('255.255.254.0')
print transferNetmask2Prefix('255.255.255.0')
print transferNetmask2Prefix('255.255.255.128')
print transferNetmask2Prefix('255.255.255.192')
print transferNetmask2Prefix('255.255.255.252')
print transferNetmask2Prefix('255.255.255.254')
print transferNetmask2Prefix('255.255.255.255')
Wish this helps. regards, Stanley Huang

Comments

Post a Comment

Popular posts from this blog

[Level 1] Reversion of git

Just read an article mentioned about the reversions of git, so take a note here. G H I J \ / \ / D E F \ | / \ \ | / | \|/ | B C \ / \ / A A = = A^0 B = A^ = A^1 = A~1 C = A^2 = A^2 D = A^^ = A^1^1 = A~2 E = B^2 = A^^2 F = B^3 = A^^3 G = A^^^ = A^1^1^1 = A~3 H = D^2 = B^^2 = A^^^2 = A~2^2 I = F^ = B^3^ = A^^3^ J = F^2 = B^3^2 = A^^3^2 reference: http://schacon.github.io/git/git-rev-parse#_specifying_revisions Wish this helps. regards, Stanley Huang
Read more

[Level 2] iif in Python

If you want to implement iif in Python, please refer to the following sample code: #!/bin/env python def iif(b): return 'It\'s True' if b else 'It\'s False' print iif(True) print iif(False) And the following sample, guess what will you get! #!/bin/env python b = True print 'b: %s' % 'Ture' if b else 'False' b = False print 'b: %s' % 'Ture' if b else 'False' Result: $ ./iif.py b: Ture False The second result is "False", not "b: False". Why??? Because the prededence of string concatenation is higher than if. Therefore you need to use () to make it correct. #!/bin/env python b = True print 'b: %s' % 'Ture' if b else 'False' b = False print 'b: %s' % ('Ture' if b else 'False') Wish this helps. regards, Stanley Huang
Read more