What Is Python's Lambda and Closure
one line anonymous function constructed on the fly
a function object that remembers values in enclosing scopes regardless of whether those scopes are still present in memory
What is Lambda?
DiveIntoPython gave a good definition. Lambda is
- a one line function
- anonymous function (no name)
- a function that can be used anywhere a function is required
- it takes in arbitrary parameters
- and implicitly return as a single expression
But most important, you need not use lambda.
Lambda is a style. You need not use it.
What’s more, if you need multiple lines, then consider a normal function. Python can pass function as parameter anyway.
Why do we have Lambda?
You might wonder why is there lambda in the first place.
This post on Python history explained well.
In 1994, lambda operator was introduced for creating anonymous functions (as expressions). Lack of a better choice..
However, the choice of the terminology “lambda” had many unintended consequences. It doesn’t match the expectation from other languages. Hence it is usually considered “sorely lacking” in features. eg. It does not work with surrounding codes.
Lambda is no closure like other languages.
What is Closure?
Best explained in ShutUpAndShip,
A CLOSURE is a function object that remembers values in enclosing scopes regardless of whether those scopes are still present in memory.
In another shorter explanation,
A closure is data attached to code
- Methods are closures
- Functions are NOT closures
- Lambda is NOT closure
Huh? Method vs Function
In case you wonder what is the difference between Method & Function,
A method is on an object. A function is independent of an object.
You define a function such as
You use a method of an object such as
obj is implicitly passed as the first parameter to the method
foo. That’s why in a class, you have a
self as the first param of a method.