maybe monad¶
- final class pythonic_fp.fptools.maybe.MayBe¶
Bases:
GenericMaybe Monad
Data structure wrapping a potentially missing item.
immutable semantics
can store any item of any type, including
Nonehashable
- __init__() None¶
- __init__(data: D) None
init
Initialize MayBe with 1 or 0 data items.
- param data:
Optional data item for the MayBe instance.
Important
A
MayBeis immutable once initialized.MayBe() is not a singleton.
- __hash__() int¶
hash
If contained item hashable, use its hash value in the hash calculation, otherwise use item’s identity.
should be safe, the MayBe holds a reference to the item.
Lazily calculates hash value, then caches it.
- __bool__() bool¶
bool
Truthy when not empty.
- returns:
True if not empty, False if empty.
- __len__() int¶
len
Zero or one items.
- __eq__(other: object) bool¶
equality comparison
Compare MayBe instance to another object. Compare first by identity, then value.
- returns:
True only if other object is a MayBe with a corresponding item, or both empty.
- __iter__() Iterator¶
iterate
- yields:
The contained item if non-empty.
- __repr__() str¶
repr string
Return the strings
‘MayBe()’ if empty
‘MayBe(repr_item)’ if not empty
Where
repr_item = repr(item).- returns:
A string to reproduce the MayBe.
- __str__() str¶
user string
Return the strings
‘MayBe(str_item)’ when not empty
‘MayBe()’ when empty
Where
str_item = str(item).- returns:
A string meaningful to an end user.
- get() D¶
- get(alt: D) D
get
Return the item if it exists, otherwise an optional alternate item.
- param alt:
Optional alternative item to return if MayBe empty.
- returns:
The item if it exists.
- raises ValueError:
When an alternate item is not provided but needed.
Warning
Unsafe method get will raise ValueError() if the MayBe is empty and an alternate return item not provided.
Tip
Best practice is to first check the MayBe in a boolean context. Threadsafe since a MayBe is immutable once created.
- map(f: Callable[[D], U]) MayBe¶
map
Map function f over the MayBe.
- param f:
Mapping function.
- returns:
A new MayBe instance if not empty, otherwise itself.
- map_except(f: Callable[[D], U]) MayBe¶
map_except
Map function f over the MayBe.
- param f:
Mapping function.
- returns:
New MayBe instance if not empty and exception is not thrown, an empty Maybe if exception is thrown, otherwise itself.
Note
Swallows exceptions of types
LookupError
ValueError
ArithmeticError
RuntimeError
Does not attempt to stop exceptions
TypeError
AttributeError
KeyboardInterrupt
- bind(f: Callable[[D], MayBe]) MayBe¶
bind
Flatmap function f over the MayBe.
- param f:
Function to bind.
- returns:
A new MayBe instance if not empty, otherwise itself.
- bind_except(f: Callable[[D], MayBe]) MayBe¶
bind_except
Flatmap function f over the MayBe.
- param f:
Function to bind over contained values.
- returns:
A successfully bound MayBe[U], a propagated
empty MayBe[U], or an empty MayBe[U] if an exception is raised.
Note
Swallows exceptions of types
LookupError
ValueError
ArithmeticError
RuntimeError
Does not attempt to stop exceptions
TypeError
AttributeError
KeyboardInterrupt
- static sequence(iterable_mb_u: Iterable[MayBe]) MayBe[Iterable]¶
MayBe.sequence
Iterable[MayBe[U]] -> MayBe[Iterable[U]]
- param sequence_mb_u:
An Iterable of MayBe[U] values.
- returns:
Empty MayBe if one of the MayBe is empty, otherwise a MayBe of an Iterable of the contained values.
Note
A sequenced empty Iterable[MayBe[U]] would produce a MayBe of an empty Iterable, not an empty MayBe.