Description:

placeholder 1.5

A placeholder uses operator overloading to create partially bound functions on-the-fly. When used in a binary expression, it will return a callable object with the other argument bound. It's useful for replacing lambda in functional programming, and resembles Scala's placeholders.
Usage
from placeholder import _ # single underscore

_.age < 18 # lambda obj: obj.age < 18
_[key] ** 2 # lambda obj: obj[key] ** 2

Note _ has special meaning in other contexts, such as the previous output in interactive shells. Assign to a different name as needed. Kotlin uses it, but in Python it is a common short name for an iterator.
_ is a singleton of an F class, and F expressions can also be used with functions.
from placeholder import F

-F(len) # lambda obj: -len(obj)

All applicable double underscore methods are supported.
Performance
Every effort is made to optimize the placeholder instance. It's 20-40x faster than similar libraries on PyPI.
Placeholders are also iterable, allowing direct access to the underlying functions.
(func,) = _.age # operator.attrgetter('age')

Performance should generally be comparable to inlined expressions, and faster than lambda. Below are some example benchmarks.
min(data, key=operator.itemgetter(-1)) # 1x
min(data, key=_[-1]) # 1.3x
min(data, key=lambda x: x[-1]) # 1.6x

Installation
% pip install placeholder

Tests
100% branch coverage.
% pytest [--cov]

License

For personal and professional use. You cannot resell or redistribute these repositories in their original state.

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