Lambda Functions in Python

Lambdas are small, anonymous functions defined with lambda params: expr. They evaluate a single expression and return its value.

Basics

Use lambdas for short callbacks and functional pipelines.

add1 = lambda x: x + 1
mul = lambda a, b: a * b

They return the expression result implicitly.

When to use vs def

• Use lambda for tiny, inline functions
• Use def for anything non‑trivial (multiple lines, statements, annotations, docstrings)

With higher‑order functions

Pass lambdas to sorted, map, filter, etc.

names = ["ada", "Guido", "Bjarne"]
print(sorted(names, key=lambda s: s.lower()))

Closures and late binding

Lambdas capture variables from the enclosing scope; late binding means the variable is looked up when the lambda runs.

funcs = [(lambda i=i: i) for i in range(3)]  # capture current i via default
[f() for f in funcs]  # [0,1,2]

Limitations

• Expression only: no statements (e.g., no assignment)
• Readability suffers beyond very simple cases; prefer def

Alternatives

• functools.partial for binding some arguments

from functools import partial
pow2 = partial(pow, exp=2)  # Python 3.8+: keyword-only in positional-only contexts may vary

Summary

• Lambdas are handy for short, inline functions
• Beware late binding; prefer def when logic grows or needs documentation