CODEWITHSUNDEEP
pythonboto
bluethundr
bluethundr

Reputation: 1325

Test Multiple Conditions in Python Try statement

I'm getting a list of aws ec2 instances with these command:

response = ec2.describe_instances()
for reservation in response["Reservations"]:
    for instance in reservation["Instances"]:

I need to see if each instance has a Private IP and a Public IP. If I use a try statement for both I get a syntax error:

try instance['PrivateIpAddress']  and instance['PublicIpAddress']:

This is the error:

File ".\aws_ec2_list_instances.py", line 26
    try instance['PrivateIpAddress']  and instance['PublicIpAddress']:
               ^
SyntaxError: invalid syntax

If I use an if statement instead of a try, python complains that the key doesn't exist if the machine doesn't have a public ip:

if instance['PrivateIpAddress'] and instance['PublicIpAddress']:

I get this error:

Traceback (most recent call last):
  File ".\aws_ec2_list_instances.py", line 26, in <module>
    if instance['PrivateIpAddress'] and instance['PublicIpAddress']:
KeyError: 'PublicIpAddress'

What's the right way to go about this?

Upvotes: 0

Views: 2663

Answers (2)

tobias_k
tobias_k

Reputation: 82899

You should check if the key is in the dictionary:

if 'PrivateIpAddress' in instance and 'PublicIpAddress' in instance:

Note, that this will just test whether those keys are present in the dictionary, but not if they have a meaningful value, e.g. depending on how you get your data they might be None or empty strings "". Alterantively, you could also use get to get the values, or None if they are not present.

if instance.get('PrivateIpAddress') and instance.get('PublicIpAddress'):

Here, the values are implicitly interpreted as bool, i.e. both None (or not-present) and empty string values would be considered False.

Upvotes: 2

Luke
Luke

Reputation: 774

Try statements are used for capturing various exceptions, such as the KeyError. You'd use them as such:

try:
    if instance['PrivateIpAddress'] and instance['PublicIpAddress']:
        # do something
except KeyError:
        # do something else

Upvotes: 1

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