Lambdas In Python

2 min readFeb 11, 2022

The aim of this tutorial🔍 is to introduce anonymous/lambda functions in Python just to make sure they work in the Higher-Order Functions lecture of SICP. You just want a simple callable object without the bureaucratic overhead of

def statement
code block it introduces

Often, an anonymous object is known as lambda (in programming, math, and Python) does the trick. The etymology is covered in Why is lambda calculus named after that specific Greek letter? and, I tend to go with

in Church’s words, the reasoning was “eeny, meeny, miny, moe” — in other words, an arbitrary choice for no reason

— https://math.stackexchange.com/a/2095748

1. PROPERTIES

Unlike lambda forms in other languages, where they add functionality, Python lambdas are only a shorthand notation if you’re too lazy to define a function.

Design and History FAQ — Python 3.9.1 documentation

restrictive
minimal
in python, synonymous with anonymous functions
introduce it with lambda instead of def
support multiple args
constrained to a single expression

lambda args: expression

2. LAMBDA AS FUNCTION EXPRESSION

lambda is itself an expression resulting in a callable object
lambda can be assigned to a binding and thus actually get a name

note that a VScode linter does rephrase this into a function declaration

3. LAMBDA VS DEF KEYWORDS

4. USAGES

tiny in size
needed for a short time
possibly, the content of a lambda itself is more expressive than a potential name
usually, they are passed an argument in other functions

5. EXAMPLE: LAMBDA AS PARAMETER FOR HIGHER-ORDER FUNCTIONS (HOF)

the HOF summationRecursive from SICP returns the same result for sumInt(a,b) as well as for sumIntLambda(a,b)

6. EXAMPLE: LAMBDA AS PARAMETER / MAP FUNCTION IN SORTED BUILTIN

sorted builtin is used for sorting iterable series
the optional key argument must be a callable

sorted(<iterable>,key=<callable>)

the key works as a mapping function that transforms the iterable as required

that lambda name: name.split()[-1] does is a mapping function to transform individual list items+
…and sorting will be done based on the transformed values, in the example above you are sorting

"turing", "gates"