如何使用itertools将返回的值从一个函数传递给另一个函数？

Question

I have a list being returned as

[('10.12.250.29', 'pdx02-he-trial-ansible01', 'us-west-2a', 'vol-e7775a10'), ('10.12.32.22', 'pdx02-cloud-prod-ansible01 Clone ', 'us-west-2b', 'vol-b0607d70'), ('10.12.0.20', 'pdx02-cloud-trial/dev-ansible01', 'us-west-2a', 'vol-b32e5c46'), ('10.12.250.7', 'pdx02-he-prod-ansible01', 'us-west-2a', 'vol-fd94400b'), ('10.12.250.4', 'pdx02-he-dev-ansible01', 'us-west-2a', 'vol-ee6abf18'), ('10.12.32.16', 'pdx02-cloud-prod-ansible', 'us-west-2b', 'vol-ae49adbb'), ('10.121.15.22', 'ansible-classic', 'us-west-2a', 'vol-f893c20d'), ('10.17.15.145', 'pdx01-ms-dev-ansible', 'us-west-2a', 'vol-e2d45515'), ('10.21.32.27', 'fra01-cloud-prod-ansible', 'eu-central-1b', 'vol-5f86f5bd'), ('10.21.250.13', 'fra01-he-trial-ansible01', 'eu-central-1a', 'vol-f9e7d220'), ('10.21.250.27', 'fra01-he-dev-ansible01', 'eu-central-1a', 'vol-f6e3fa2f'), ('10.21.0.9', 'fra01-cloud-dev-ansible01', 'eu-central-1a', 'vol-98104671'), ('10.21.250.5', 'fra01-he-prod-ansible01', 'eu-central-1a', 'vol-809b8259'), ('10.31.250.26', 'sin01-he-dev-ansible01', 'ap-southeast-1a', 'vol-86443940'), ('10.31.250.19', 'sin01-he-prod-ansible01', 'ap-southeast-1a', 'vol-bebcc178'), ('10.31.32.12', 'sin01-cloud-prod-ansible01', 'ap-southeast-1b', 'vol-01409de9'), ('10.31.250.27', 'sin01-he-trial-ansible01', 'ap-southeast-1a', 'vol-f6cdc631'), ('10.31.0.18', 'sin01-cloud-dev-ansible01', 'ap-southeast-1a', 'vol-3c0aac28')]

this is basically:

<IP_ADDRESS> , <AWS_TAG_NAME> , <REGION> , <VOLUME>

now I passed it to another method where I need to extract each value and store it individually so I used itertools from __main__ :

data = list(itertools.chain(*ansible_box_info))
print "-----------------"
print data
#mapping = {i[0]: [i[1], i[2]] for i in data}
print "Now Calling the Snapshot Creater!"
call_snapshot_creater(data)

def call_snapshot_creater(passed_data):
    ip_address = ','.join(list(itertools.chain(*[[j[0] for j in i] for i in data])))
    tags_descrip = list(itertools.chain(*[[j[1] for j in i] for i in data]))
    regions_az = list(itertools.chain(*[[j[2] for j in i] for i in data]))
    volume_id = list(itertools.chain(*[[j[3] for j in i] for i in data]))

This breaks the above list and picks just the first letter of everything , ie the ip_address prints :

1,p,u,v,1,p,u,v,1,p,u,v,1,p,u,v,1,p,u,v,1,p,u,v,1,a,u,v,1,p,u,v,1,f,e,v,1,f,e,v,1,f,e,v,1,f,e,v,1,f,e,v,1,s,a,v,1,s,a,v,1,s,a,v,1,s,a,v,1,s,a,v

instead of 10.12.250.29 , 10.12.32.22 .................. and same for others

how to use the iterators to break this correctly ?

I am trying to create snapshots by passing these values to my snapshot creator :

def call_snapshot_creater(passed_data):
    ip_address = ','.join(list(itertools.chain(*[[j[0] for j in i] for i in data])))
    tags_descrip = list(itertools.chain(*[[j[1] for j in i] for i in data]))
    regions_az = list(itertools.chain(*[[j[2] for j in i] for i in data]))
    volume_id = list(itertools.chain(*[[j[3] for j in i] for i in data]))

    regions = ['us-west-2', 'eu-central-1', 'ap-southeast-1']

    for region in regions:
        ec2 = boto3.resource('ec2', region, aws_access_key_id=ACCESS_KEY, aws_secret_access_key=SECRET_KEY, )
        print "Snapshot Creation For Ansible -> ",ip_address," initiated , tag = ", tags_descrip ,"region : ", regions_az
        print "Snapshot will be created with -> Name : ",tags_descrip
        snapshot = ec2.create_snapshot(VolumeId=volume_id, Description=tags_descrip)
        print snapshot.id
        print "Snapshot is being created for Ansible box ", tags_descrip ,"with snapshot id :",snapshot.id
        #slack.chat.post_message(slack_channel,"Creating Snapshot for The volume"+ str(snapshot.id),username='Ansible_box_snapshot_bot')
        snapshot.load()
        while snapshot.state != 'completed':
            print "The Snapshot :", snapshot.id , "for Ansible box named : ", tags_descrip  ,"is currently in :",snapshot.state," state"
            time.sleep(30)
            snapshot.load()
            print snapshot.progress
        else:
            print "Snapshot ",snapshot.id, "for Ansible box ", tags_descrip , "is now Ready!! Final state ->",snapshot.state

Answer 1

with [[j[0] for j in i] for i in data] you are going through the list, and calculate [j[0] for j in i] , where i is the current tuple. So you iterate through the tuple, where j is the current string, and you get the first character of that string.

What you want however, is only the first item of the tuple. This means that you don't even need itertools.chain : Do it with [i[0] for i in data] . This gets the first element of each tuple, and yields the expected output.

So here is the changed code:

ip_address = ','.join(i[0] for i in data)  # you can use an iterator here
tags_descrip = ','.join(i[1] for i in data)
regions_az = ','.join(i[2] for i in data)
volume_id = ','.join(i[3] for i in data)

This can, however, all be done in one line:

ip_address, tags_descrip, regions_az, volume_id = (','.join(j[i] for j in data) for i in range(4))

Another possibility would be following: (Here you only iterate over data once, but it isn't that readable)

ip_address, tags_descrip, regions_az, volume_id = map(','.join, zip(*data))

Here is how the second one works (I think the first one is self explanatory):

You pass following tuples to zip :

IP, ... from the first tuple
IP, ... from the second tuple
   .
   .
   .

So all the different fields are aligned. zip gives you an iterator, that returns the tuple containing the first items of each list, then a tuple containing the second items, and so on. So if you would call list(zip(*data)) , you would have a list with for entries: All the IP's, and so on.

I would choose the first option over the second one, because the first one is a whole lot more readable, but if you really care for performance (but you wouldn't use Python in this case, I suppose), the second one is the way to go.

I hope I could help,

CodenameLambda

Answer 2

You are not using chain and unpacking correctly. All you are trying to do, can be done with zip and unpacking viz. zip(*...) :

>>> l = [('10.12.250.29', 'pdx02-he-trial-ansible01', 'us-west-2a', 'vol-e7775a10'), ('10.12.32.22', 'pdx02-cloud-prod-ansible01 Clone ', 'us-west-2b', 'vol-b0607d70'), ('10.12.0.20', 'pdx02-cloud-trial/dev-ansible01', 'us-west-2a', 'vol-b32e5c46'), ('10.12.250.7', 'pdx02-he-prod-ansible01', 'us-west-2a', 'vol-fd94400b'), ('10.12.250.4', 'pdx02-he-dev-ansible01', 'us-west-2a', 'vol-ee6abf18'), ('10.12.32.16', 'pdx02-cloud-prod-ansible', 'us-west-2b', 'vol-ae49adbb'), ('10.121.15.22', 'ansible-classic', 'us-west-2a', 'vol-f893c20d'), ('10.17.15.145', 'pdx01-ms-dev-ansible', 'us-west-2a', 'vol-e2d45515')]
>>>
>>> data = zip(*l)
>>>
>>> ip_address = ','.join(next(data))
>>> ip_address
'10.12.250.29,10.12.32.22,10.12.0.20,10.12.250.7,10.12.250.4,10.12.32.16,10.121.15.22,10.17.15.145'
>>>
>>> tags_descrip = ','.join(next(data))
>>> tags_descrip
'pdx02-he-trial-ansible01,pdx02-cloud-prod-ansible01 Clone ,pdx02-cloud-trial/dev-ansible01,pdx02-he-prod-ansible01,pdx02-he-dev-ansible01,pdx02-cloud-prod-ansible,ansible-classic,pdx01-ms-dev-ansible'
>>>
>>> regions_az = ','.join(next(data))
>>> regions_az
'us-west-2a,us-west-2b,us-west-2a,us-west-2a,us-west-2a,us-west-2b,us-west-2a,us-west-2a'
>>>
>>> volume_id = ','.join(next(data))
>>> volume_id
'vol-e7775a10,vol-b0607d70,vol-b32e5c46,vol-fd94400b,vol-ee6abf18,vol-ae49adbb,vol-f893c20d,vol-e2d45515'