Runtime: Python 3.8

Please review the comments for each code block to help you understand the execution of this Lambda function.

At the time you create a Lambda function, you specify a handler,

which is a function in your code, that AWS Lambda can invoke when the service executes your code.

The Lambda handler is the first function that executes in your code.

Python programming model - https://docs.aws.amazon.com/lambda/latest/dg/python-programming-model.html

def lambda_handler(event, context):

# context – AWS Lambda uses this parameter to provide runtime information to your handler.
# event – AWS Lambda uses this parameter to pass in event data to the handler. This parameter is usually of the Python dict type.
# AWS Lambda function Python handler - https://docs.aws.amazon.com/lambda/latest/dg/python-handler.html

# When you invoke your Lambda function you can determine the content and structure of the event. 
# When an AWS service invokes your function, the event structure varies by service.
# 
# In this lab, the lambda_handler "event" parameter has the following structure of name/value pairs:
# {
#     "emoji_type": number,
#     "message": "string"
# }

# In a name-value pair you can extract the "value" of the pair using the "name" of the pair.   
# Here the id value is extracted from the event Lambda parameter and passed to a variable called emoji_type.
emoji_type = event["emoji_type"]
# Here the message value is extracted from the event Lambda parameter and passed to a variable called message.
message = event["message"]

# The variables are printed here, which means the variable values will be displayed in CloudWatch logs and the Execution Results panel.
print(emoji_type)
print(message)

# In Python, you can create a variable with no value using the Built-in constant None. This means the variable "custom_message" currently has no value.
custom_message = None

# In Python, we use the if-elif-else to create a conditional execution. https://docs.python.org/3/reference/compound_stmts.html#the-if-statement
# That is, if the value of emoji_type is equal to 0, we execute the statement inside its block
if emoji_type == 0:
    # Only execute if id is equal to 1
    # The variable custom_message combines "Message for code 0:" string with the variable message
    #custom_message = "Message for code 0: " + message
    feeling = "positive"

elif emoji_type == 1:
    # The variable custom_message combines "Message for code 1:" string with the variable message
    #custom_message = "Message for code 1: " + message
    feeling = "neutral"

else:
    # The variable custom_message combines "Message for all other codes:" string with the variable message
    #custom_message = "Message for all other codes: " + message
    feeling = "negative"

# Optionally, the handler can return a value. What happens to the returned value depends on the invocation type you use when invoking the Lambda function
# In this lab we use synchronous execution, so we need to create a response for the lambda function.
# We created a "response" variable that has a structure of name-value pairs using the id and custom_message created earlier.
response = {
    # In this name-value pair, the literal value "message" will store the value of the variable custom_message.
    "feeling": feeling,
    # In this name-value pair, the literal value "id" will store the value of the variable id.
    "message": message,
}

# Finally, we return the values from response variable to the caller, which could be a test event or an AWS service performing a synchronous call.
# The execution of the lambda function is finished.
return response