Working with Lambda Code
amazon web services - Where in S3 my Lambda code stored - Stack Overflow
amazon web services - AWS- AWS command to view lambda function in Command Line - Stack Overflow
amazon web services - Download an already uploaded Lambda function - Stack Overflow
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When you have a "large" lambda, you upload it to AWS and you cannot preview the code in the AWS Lambda console. What are ways that we can edit the code and update it faster? How do you guys do it? Do you mind sharing them?
If you upload your source code to your own S3 bucket before creating the Lambda function, then you will know the path to your source code. Note that simply editing the code in S3 will not update your Lambda function. See link below. Amazon will copy your code from your bucket to Amazon's S3 bucket.
If you upload your code in the AWS console when you create the Lambda function, then it is stored in an Amazon S3 location that you cannot access.
The end result is that your code is located in a private Amazon S3 bucket that you cannot access.
AWS Lambda Function Code
The Lambda service stores your code encrypted in an S3 bucket. AWS doesn't provide any more specific information than that. It's possible that the service has its own S3 bucket(s) and they individually encrypt all objects that they store there.
No, you can't access the Lambda service's S3 bucket(s) directly, but you can download the code you previously uploaded to your Lambda function. Go to the AWS Lambda console, select your Lambda function, then click Actions | Export function, then click Download deployment package. Note: if your code was written in Java (or other compiled language) then the download will contain compiled files, not the original source code.

Yes!
Navigate over to your lambda function settings and on the top right you will have a button called "Actions". In the drop down menu select "export" and in the popup click "Download deployment package" and the function will download in a .zip file.
Action button on top-right

A popup from CTA above (Tap "Download deployment package" here)

Update: Added link to script by sambhaji-sawant. Fixed Typos, improved answer and script based on comments!
You can use aws-cli to download the zip of any lambda.
First you need to get the URL to the lambda zip
$ aws lambda get-function --function-name $functionName --query 'Code.Location'
Then you need to use wget/curl to download the zip from the URL.
$ wget -O myfunction.zip URL_from_step_1
Additionally you can list all functions on your AWS account using
$ aws lambda list-functions
I made a simple bash script to parallel download all the lambda functions from your AWS account. You can see it here :)
Note: You will need to setup aws-cli before using the above commands (or any aws-cli command) using aws configure
Full guide here