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Python implementation of Scala-like monadic data types.

Project description

Functional Python - Scala-like monadic data types

Functional Python is a framework which implements Scala-like monadic data types, such as Option or Map.

Why?

Method chaining
# ToDo: Example
Type Safety
# ToDo: Example

Api Description

Options

Represents optional values. Instances of Option are either an instance of Some or the object None. Options are generics of single type parameter.

Creating an Option
from functional.option import *

# Scala-like constructor
x = Some(4)      # Some(4)
y = Option.empty # None
z = none         # None

# Python-like constructor
x = Option(4)    # Some(4)
y = Option(None) # None

Note that None which is printed is not Python None but is special object which does not contain any value and equals to Option(None).

Getting value of an Option

Options implement .get property and .getOrElse(default) method. First one checks Option is not empty and either returns value or throws an exception. Second one returns default instead of throwing an exception.

from functional.option import *
x = Some(4)      # Some(4)
y = none         # None

x.get            # 4
y.get            # raises EmptyOption

x.get_or_else(5) # 4
y.get_or_else(5) # 5

# .is_defined returns True if Option is not None
x.is_defined     # True
y.is_defined     # False

# .is_empty is the opposite
x.is_empty       # False
y.is_empty       # True

# .non_empty is the same as .is_defined
x.non_empty      # True
y.non_empty      # False

Note that unlike in Scala, this Option's .get_or_else is not lazy-evaluated, so this code will fail:

Some(4).get_or_else(1/0)

To prevent, it is recommended use python-like accessors (see below).

Mapping an Option

Options are both functors and monads, meaning they possess .map() and .flat_map() methods with the following signatures (where object is a type Option[A]):

  • .map(f: A => B): Option[B] - map value inside an Option.
  • .flat_map(f: A => Option[B]): Option[B] - map value inside an Option to an Option.

Both these methods work only on non-empty options, returning Option.empty for otherwise.

from functional.option import *
x = Some(4)            # Some(4)
y = none               # None
z = Some(6)            # Some(6)

x.map(lambda v: v + 2) # Some(6)
y.map(lambda v: v + 2) # None
z.map(lambda v: v + 2) # Some(8)

x.flat_map(lambda v: Some(v) if v < 5 else none) # Some(4)
y.flat_map(lambda v: Some(v) if v < 5 else none) # None
z.flat_map(lambda v: Some(v) if v < 5 else none) # None
Flattening an Option

Sometimes you get an Option which contains Option. There is special property .flatten which converts Option[Option[T]] into Option[T]

# ToDo: Example
Python-style accessors

Options support python-like accessors / converters __bool__, __iter__, __len__, and __enter__/__exit.

# ToDo: Example

Map

TODO

Plans

  • Test coverage
  • Support Maps (both mutable and immutable)
  • Support Lists (both mutable and immutable)

Project details


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