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The names "lambda abstraction", "lambda function", and "lambda expression" refer to the notation of function abstraction in lambda calculus, where the usual function f (x) = M would be written (λx. M), and where M is an expression that uses x. Compare to the Python syntax of lambda x: M.
In Python, functions are first-class objects that can be created and passed around dynamically. Python's limited support for anonymous functions is the lambda construct. An example is the anonymous function which squares its input, called with the argument of 5:
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
An internal iterator is a higher-order function (often taking anonymous functions) that traverses a collection while applying a function to each element. For example, Python's map function applies a caller-defined function to each element:
The examples 1 and 2 denote different terms, differing only in where the parentheses are placed. They have different meanings: example 1 is a function definition, while example 2 is a function application. The lambda variable x is a placeholder in both examples. Here, example 1 defines a function .
Python had support for "lambda", "map", ... Compared with relational syntax, functional syntax is a more compact notation for nested functions. For example, the ...
An example of such a function is the function that returns 0 for all even integers, and 1 for all odd integers. In lambda calculus , from a computational point of view, applying a fixed-point combinator to an identity function or an idempotent function typically results in non-terminating computation.
To apply such a function object, one must use the funcall function: (funcall #'foo bar baz). Python Explicit partial application with functools.partial since version 2.5, and operator.methodcaller since version 2.6. Ruby The identifier of a regular "function" in Ruby (which is really a method) cannot be used as a value or passed.