Lambda Function
Last Updated: July 29, 2026 | By Mihail Sebastian | AI Dictionary
A term with two meanings: an anonymous inline function in languages like Python, and AWS Lambda, a service that runs code without managing servers.
What is a Lambda Function?
A lambda function is a small anonymous function defined inline, without a name, in languages like Python. The same phrase also names something unrelated: AWS Lambda, Amazon’s serverless service that runs code in response to events with no server to manage.
Which one a document means depends on context. Code discussions almost always mean the language feature; infrastructure and MLOps discussions usually mean the AWS service.
Lambda Functions in Python
Python’s lambda keyword defines a function in a single expression, used where a full def would be ceremony: as a sorting key, inside map() and filter(), or in a pandas transformation.
sorted(preds, key=lambda p: p["confidence"], reverse=True)
That line orders a model’s predictions by confidence. The lambda exists only for that call; it takes an argument, returns a value, and has no name.
AWS Lambda: Serverless Functions
AWS Lambda runs a function you upload whenever a trigger fires (an HTTP request, a file landing in storage, a queue message) and bills only for execution time. No server runs between invocations.
For ML systems it suits light, bursty work: preprocessing uploaded files, calling a hosted model API, or handling a webhook when a training job finishes. Heavy inference fits less well because of memory limits and cold starts.
Example of a Lambda Function
A data scientist cleans a labeled dataset in pandas before training. One column mixes cases (“Cat”, “cat”, “CAT”), so she normalizes it with a one-line lambda:
df["label"] = df["label"].apply(lambda x: x.strip().lower())
Every row passes through the anonymous function, and the labels come out consistent. A named function would work identically; the lambda keeps a three-second transformation inline, right where it is used.
Related AI terms: Webhook · Pandas · Inference · Deploy
Did you like the Lambda Function gist?
Learn about 250+ need-to-know artificial intelligence terms in the AI Dictionary.
Mihail Sebastian — Writes about AI governance, regulation, and the technology behind them. Placeholder bio — replace with a real credential line. About