How parsing of dictionary in python works?-CodePudding

I have below template.yaml file:

Resources:
  ApiGatewayDeployment:
    Type: AWS::ApiGateway::Deployment
    Properties:
      RestApiId: ApiGateway

When I am trying to parse it using below python code:

import pathlib
import yaml


def main():
    template_file = pathlib.Path('template.yaml')
    cfn = yaml.safe_load(template_file.read_text())
    for res in cfn["Resources"]:
        print(res)


if __name__ == "__main__":
    main()

I am getting key as output:

ApiGatewayDeployment

But when I am parsing it using below code:

import pathlib
import yaml


def main():
    template_file = pathlib.Path('template.yaml')
    cfn = yaml.safe_load(template_file.read_text())
    for res in cfn["Resources"],:
        print(res)


if __name__ == "__main__":
    main()

I am getting dictionary as output:

{'ApiGatewayDeployment': {'Type': 'AWS::ApiGateway::Deployment', 'Properties': {'RestApiId': 'ApiGateway'}}}

Can anyone please explain this logic?

Edit: updated 2nd python code

CodePudding user response：

This doesn't have anything to do with how the dictionary is parsed, but rather the way that you're trying to iterate over its contents. The difference is a single comma:

for res in cfn["Resources"]:

vs:

for res in cfn["Resources"],:

Adding a trailing comma to an expression turns it into a tuple (i.e. it adds another level of container to it).

In the first version, res is iterating over the keys of cfn["Resources"]. (Note: you might want to iterate over cfn["Resources"].values() instead!)

In the second version, res is iterating over a tuple that contains cfn["Resources"] itself.

Hence:

    for res in cfn["Resources"],:
        print(res)

is exactly equivalent to just doing:

    print(cfn["Resources"])

Here's a simpler example using a regular old list:

>>> arr = [1, 2, 3]
>>> for i in arr:
...     print(i)
...
1
2
3
>>> for i in arr,:  # note the comma!
...     print(i)
...
[1, 2, 3]