Analysis and Solution for 'No module named lambda_function' Error in AWS Lambda Python Deployment

Problem Background and Error Analysis

During AWS Lambda Python function deployment, developers often encounter the Runtime.ImportModuleError: Unable to import module 'lambda_function': No module named lambda_function error. This error indicates that the AWS Lambda runtime cannot find the specified module entry point, typically due to improper file naming or handler configuration.

Core Issue: Filename and Handler Configuration

According to AWS Lambda's default configuration, the console automatically sets the handler to "lambda_function.lambda_handler". This means AWS Lambda attempts to import a module named lambda_function and call the lambda_handler function within it. If the actual filename does not conform to this convention, import errors occur.

Solution 1: Correct File Naming

Ensure the Python file is named lambda_function.py and contains a function named lambda_handler. Below is the corrected code example:

import json
import boto3
import urllib.parse

print('Loading function')

s3 = boto3.client('s3')

def lambda_handler(event, context):
    # Get the object from the event and show its content type
    bucket = event['Records'][0]['s3']['bucket']['name']
    key = urllib.parse.unquote_plus(event['Records'][0]['s3']['object']['key'])
    
    try:
        response = s3.get_object(Bucket=bucket, Key=key)
        s3.download_file(bucket, key, '/tmp/data.txt')
        
        with open('/tmp/data.txt', 'r') as file:
            lines = [line.rstrip('\n') for line in file]
            
        for line in lines:
            columns = line.split(',')
            print(columns[5], columns[6])
            
        print("CONTENT TYPE: " + response['ContentType'])
        return response['ContentType']
        
    except Exception as e:
        print(e)
        error_message = f'Error getting object {key} from bucket {bucket}. Make sure they exist and your bucket is in the same region as this function.'
        print(error_message)
        raise e

Solution 2: Custom Handler Name

If you prefer to use a different filename, you can explicitly set the handler name after creating the Lambda function. For example, if the filename is my_function.py and the handler function is named main_handler, the handler should be configured as "my_function.main_handler".

Packaging Considerations

When creating the deployment package, ensure you correctly package the contents of the project directory rather than the directory itself. Incorrect packaging can lead to file hierarchy issues, causing module import errors. Proper packaging steps include:

1. Navigate to the project directory
2. Select all files and subdirectories
3. Create a ZIP archive
4. Upload to AWS Lambda

Dependency Management Best Practices

Beyond file naming issues, ensure all dependencies are properly packaged. For external dependencies like the requests library, it's recommended to manage dependencies using a requirements.txt file and install them in the project directory using pip install -r requirements.txt -t ..

Testing and Verification

After deployment, test the function using the AWS console or CLI tools. Successful execution should display function loading information and process event data normally. If errors persist, check CloudWatch logs for detailed error information.

Conclusion

The No module named lambda_function error typically stems from simple configuration issues. By ensuring correct file naming, handler configuration, and packaging methods, these problems can be quickly resolved. Understanding AWS Lambda's module import mechanism is crucial for successful Python function deployment.