Python Forum

I am begenning DevNet from a pure Networking background. I have some code I'm looking at from 'Network Programmability and Automation' book. Don't know how '

temp['name'] = name

' works.

vlans_list = [
    'vlan 10', 'name DATA', 'vlan 20', 'name VOICE', 'vlan 30', 'name WIRELESS'
]

vlans = []

for item in vlans_list:
    if 'vlan' in item: 
        temp = {}
        id = item.strip().strip('vlan').strip()
        temp['id'] = id
    elif 'name' in item:
        name = item.strip().strip('name').strip()
        temp['name'] = name
        vlans.append(temp)

I see strip stripping off vlan and whitespace with the string of strips. Then the string is left with only '10' as in the first string in vlans_list. I don't know where id comes from. Does

var['string'] = 'string'

write the value declared for that line in the iteration? I cannot find this usage in documentation. Basically this script is replacing/stripping 'vlan' for 'id', but code confuses me no matter how simple it seems.

temp is a dict. A dict can have any hashable object as a key, including strings. temp['name'] = name assigns the value associated with the variable name to the key 'name' in temp. Stepping through the code:

vlans_list = [
    'vlan 10', 'name DATA', 'vlan 20', 'name VOICE', 'vlan 30', 'name WIRELESS'
]
 
vlans = []
 
for item in vlans_list:                           # loop through vlans_list, assigning each member to item
    if 'vlan' in item:                            # check for vlan being in the string
        temp = {}                                 # create a new dictionary
        id = item.strip().strip('vlan').strip()   # remove vlan from the string, assign the result to id
        temp['id'] = id                           # store id in the new dictionary (key = 'id')
    elif 'name' in item:                          # check for name being in the string
        name = item.strip().strip('name').strip() # remove 'name' from the string, assign it to variable name
        temp['name'] = name                       # store name in the dictionary.
        vlans.append(temp)                        # store the dictionary with the vlan info in a list

Each vlan ends up with it's own dictionary in the list vlans.

(Aug-07-2019, 05:25 PM)ichabod801 Wrote: [ -> ]temp['id'] = id                           # store id in the new dictionary (key = 'id')

So if you state dictionary['string'] = 'string', Python will insert your string in the line you are on in the iteration? In other words, It is stating the string 'id' is == to the var id from the previous line because dictionaries are key/value pairs and the key == the value?

No. The part you got right is that dictionaries are key/value pairs. temp['id'] = id associates (the value in the variable id) with the key 'id' in the dictionary temp. Now that value will be returned when you use temp['id'].

one more question: why isn't it instead written as

temp{'id'} = id

since temp is a dictionary and not a list and the iteration is for one dictionary obj in the overall vlans list?

Why would it be written like that? It's written the way it is because that made sense to Guido.

You keep using the work iteration, I don't think you understand what it means. This:

temp['id'] = id

Is assigning to an index. That assigns a single value to a single key in the dictionary. This is plain old indexing (getting a single value out of a dictionary):

id = temp['id']

Iteration is for loops. So this would be iteration:

for key in temp:
    print(key, temp[key])

That gets all the keys out of the dictionary. Generally, you get all the key/value pairs out of the dictionary together with the items method:

for key, value in temp.items():
    print(key, value)

Thanks everyone for the input. I need to evaluate it and see how it makes sense to me. Give me a few