python-progressbar/progressbar/base.py at docstring-coverage · autar-pr/python-progressbar

51 lines (36 loc) · 1.37 KB

"""Sentinels for "no length known" and "no value given".

Both sentinels are *classes*, not instances, and both are falsey. That

is the whole point of `FalseMeta`: it lets the rest of the library write

`if self.max_value:` and have that mean "has a known, usable length",

without a separate `is UnknownLength` check at every site. See

`ProgressBar.data` and the update-gate logic in `progressbar.bar` for

the call sites that rely on it.

"""

from __future__ import annotations

from typing import IO, TextIO

class FalseMeta(type):

"""Metaclass making its classes evaluate as false.

Applied to the sentinels below so they can stand in for a missing

value in a boolean test rather than needing an identity comparison.

"""

@classmethod

def __bool__(cls) -> bool: # pragma: no cover

"""Report the class itself as falsey."""

return False

class UnknownLength(metaclass=FalseMeta):

"""The total amount of work is not knowable in advance.

Passed as `max_value` for an iterable with no `__len__` — a

generator, a stream — so the bar renders progress without a

percentage or an ETA.

"""

class Undefined(metaclass=FalseMeta):

"""No value was supplied, where `None` is itself meaningful."""

assert IO is not None

assert TextIO is not None

__all__ = (

'IO',

'FalseMeta',

'TextIO',

'Undefined',

'UnknownLength',

)

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