# Copyright (C) 2015-2021 Regents of the University of California
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from collections.abc import Iterable, Iterator
# 5.14.2018: copied into Toil from https://github.com/BD2KGenomics/bd2k-python-lib
from typing import Any, TypeVar
IT = TypeVar("IT")
[docs]
def flatten(iterables: Iterable[IT]) -> Iterator[IT]:
"""Flatten an iterable, except for string elements."""
for it in iterables:
if isinstance(it, str):
yield it
else:
yield from it
# noinspection PyPep8Naming
[docs]
class concat:
"""
A literal iterable to combine sequence literals (lists, set) with generators or list comprehensions.
Instead of
>>> [ -1 ] + [ x * 2 for x in range( 3 ) ] + [ -1 ]
[-1, 0, 2, 4, -1]
you can write
>>> list( concat( -1, ( x * 2 for x in range( 3 ) ), -1 ) )
[-1, 0, 2, 4, -1]
This is slightly shorter (not counting the list constructor) and does not involve array
construction or concatenation.
Note that concat() flattens (or chains) all iterable arguments into a single
result iterable:
>>> list( concat( 1, range( 2, 4 ), 4 ) )
[1, 2, 3, 4]
It only does so one level deep. If you need to recursively flatten a data structure,
check out crush().
If you want to prevent that flattening for an iterable argument, wrap it in concat():
>>> list( concat( 1, concat( range( 2, 4 ) ), 4 ) )
[1, range(2, 4), 4]
Some more example.
>>> list( concat() ) # empty concat
[]
>>> list( concat( 1 ) ) # non-iterable
[1]
>>> list( concat( concat() ) ) # empty iterable
[]
>>> list( concat( concat( 1 ) ) ) # singleton iterable
[1]
>>> list( concat( 1, concat( 2 ), 3 ) ) # flattened iterable
[1, 2, 3]
>>> list( concat( 1, [2], 3 ) ) # flattened iterable
[1, 2, 3]
>>> list( concat( 1, concat( [2] ), 3 ) ) # protecting an iterable from being flattened
[1, [2], 3]
>>> list( concat( 1, concat( [2], 3 ), 4 ) ) # protection only works with a single argument
[1, 2, 3, 4]
>>> list( concat( 1, 2, concat( 3, 4 ), 5, 6 ) )
[1, 2, 3, 4, 5, 6]
>>> list( concat( 1, 2, concat( [ 3, 4 ] ), 5, 6 ) )
[1, 2, [3, 4], 5, 6]
Note that while strings are technically iterable, concat() does not flatten them.
>>> list( concat( 'ab' ) )
['ab']
>>> list( concat( concat( 'ab' ) ) )
['ab']
"""
def __init__(self, *args: Any) -> None:
super().__init__()
self.args = args
[docs]
def __iter__(self) -> Iterator[Any]:
def expand(x):
if isinstance(x, concat) and len(x.args) == 1:
i = x.args
elif not isinstance(x, str):
try:
i = x.__iter__()
except AttributeError:
i = (x,)
else:
i = x
return i
return flatten(map(expand, self.args))
