multiline string substitution in python

February 22, 2023

I am trying this out.

account = "11111111111"
tenant_name= "Demo"
project_name= "demo"

sns_access_policy = """{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "0",
      "Effect": "Allow",
      "Principal": {
        "Service": "codestar-notifications.amazonaws.com"
      },
      "Action": "sns:Publish",
      "Resource": "arn:aws:sns:eu-west-1:{account_id}:{tenant_name}-{project_name}-pipeline-monitoring"
    }
  ]
}"""

sns_access_policy = sns_access_policy.replace("{account_id}",account).replace("{tenant_name}",tenant_name).replace("{project_name}",project_name)

This is doing my work, but I am looking something like f{string_substitution}.

sns_access_policy = f"""{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "0",
      "Effect": "Allow",
      "Principal": {
        "Service": "codestar-notifications.amazonaws.com"
      },
      "Action": "sns:Publish",
      "Resource": "arn:aws:sns:eu-west-1:{account}:{tenant_name}-{project_name}-pipeline-monitoring"
    }
  ]
}"""

I am getting an error

SyntaxError: f-string: expressions nested too deeply

is there any other way than using replace() for this?

>Solution :

When you use an f-string all those braces start an expression, but in your case they are just literal braces. You have to use double braces for that.

sns_access_policy = f"""{{
  "Version": "2012-10-17",
  "Statement": [
    {{
      "Sid": "0",
      "Effect": "Allow",
      "Principal": {{
        "Service": "codestar-notifications.amazonaws.com"
      }},
      "Action": "sns:Publish",
      "Resource": "arn:aws:sns:eu-west-1:{account}:{tenant_name}-{project_name}-pipeline-monitoring"
    }}
  ]
}}"""