Question

i read data from my config file like this:

ip_vlan1 = "10.10.($id+100).5"
ip_vlan2 = "10.11.($id*2+1).6"
v.v...

And for each vlan, I want calculate vlan address for it, based on ID and vlan-expression:

def calculate_vlan_id(id, vlan_exp):
    ...
    return ip_addr   # string

Example:

def(3, ip_vlan1) --> result: "10.10.103.5"
def(5, ip_vlan2) --> result: "10.11.11.6"

Do you have a solution for this?

Thanks in advance, folks!

Answer 1

You could use a text templating engine. (Which is safer than using eval based tricks).

Here’s an example using genshi

from genshi.template import TextTemplate
ip_vlan1 = TextTemplate("10.10.${id+100}.5")
ip_vlan2 = TextTemplate("10.11.${2*id+1}.6")
print( ip_vlan1.generate(id=3) ) # prints 10.10.103.5
print( ip_vlan2.generate(id=5) ) # prints 10.11.11.6

If you really need the calculate_vlan_id function it would look something like this:

def calculate_vlan_id(id,ip_vlan):
  return ip_vlan.generate(id=id)

Edit:

As requested here’s an example using jinja2: This may not be the best way to do this, the jinja2 docs are large and confusing.

ip_vlan1 = jinja2.Template('10.10.{{id+100}}.5')
ip_vlan2 = jinja2.Template('10.11.{{2*id+1}}.6')
ip_vlan1.render(id=3)
ip_vlan2.render(id=5)

Both these methods are untested