lverweijen / fny

Create python functions without lambda

Python is a quite capable of writing code functionally and many libraries have been written to reimplement many of the functional tools. The only obstacle left is python's ugly lambda-syntax. This library remedies this by letting one construct python functions out of thin air.

Examples

Create functions either using the fn-factory or by manipulating the it-function:

from fny import fn, lfn, it

inc2 = it + 2
inc3 = fn('+', 3)
inc2(3)  # => 5
inc3(3)  # => 6

In some cases the inverse can be constructed automatically:

dec3 = inc3.inverse
dec3(8)  # => 5

Functions with multiple arguments can be constructed as well:

add_subtract = fn(0) + fn(1) - fn(2)
add_subtract(5, 7, 3)  # => 9

Combine partially applied functions (lfn) with composition (@ is used):

dotproduct = sum @ lfn(map, fn('*'))
dotproduct([1, 2, 3], [3, 2, 1])  # => 10

A Pipe-class makes it easy to pass values around:

from fny import Pipe

fac5 = (Pipe(5)
        .into_head('+', 1)           # ^^ + 1
        .into_last(range, 1)         # range(1, ^^)
        .into_last(reduce, fn('*'))  # reduce(fn('*'), ^^)
        .value)  # => 120

Overview

Name	How
Identity function	it
Unary operations	-it, ~it
Binary operations	it + 1, fn('+', 1)
Attribute access	fn('.', "x"), it.attr.x
Method call	fn(".upper"), it.mtd.upper()
Composing functions	fn(abs) @ fn(sum)
Partially apply on the right	fn(pow, 2), fn(pow).right(2)
Partial apply on the left	lfn(pow, 2), fn(pow).left(2)
Juxtaposition	fn((math.cos, math.sin))
Constant function	fn(':=', 42)
Return nth argument	fn(n)
Container lookup	fn({'a': 1, 'b': 2, 'c': 3})
Test membership	fn(set('aeiouy'))
Flip first and second argument	fn(divmod).flip
Apply function to tuple	fn(pow).apply((2, 5))
Treat arguments as list	fn(sum).pack(1, 2, 3, 4, 5)

See also

This library aims just for function creation. To manipulate sequences, it can be combined with itertools.