cs-seq 20251231.1
Stuff to do with counters, sequences and iterables.
Requires Python: >=3
Keywords: python2, python3

Stuff to do with counters, sequences and iterables.

*Latest release 20251231.1*:
range: support range[type] returning a GenericAlias.

Note that any function accepting an iterable
will consume some or all of the derived iterator
in the course of its function.

Short summary:
* `ClonedIterator`: A thread safe clone of some orginal iterator.
* `common_prefix_length`: Return the length of the common prefix of sequences `seqs`.
* `common_suffix_length`: Return the length of the common suffix of sequences `seqs`.
* `first`: Return the first item from an iterable; raise `IndexError` on empty iterables.
* `get0`: Return first element of an iterable, or the default.
* `greedy`: A decorator or function for greedy computation of iterables.
* `imerge`: Merge an iterable of ordered iterables in order.
* `infill`: A generator accepting an iterable of objects which yields `(obj,missing_keys)` 2-tuples indicating missing records requiring infill for each object.
* `infill_from_batches`: A batched version of `infill(objs)` accepting an iterable of batches of objects which yields `(obj,obj_key)` 2-tuples indicating missing records requiring infill for each object.
* `isordered`: Test whether an iterable is ordered. Note that the iterable is iterated, so this is a destructive test for nonsequences.
* `last`: Return the last item from an iterable; raise `IndexError` on empty iterables.
* `not_none`: Filter the iterables for items which are not `None`.
* `onetomany`: A decorator for a method of a sequence to merge the results of passing every element of the sequence to the function, expecting multiple values back.
* `onetoone`: A decorator for a method of a sequence to merge the results of passing every element of the sequence to the function, expecting a single value back.
* `range`: A class like the builtin `range` exceppt that it will accept `...` as the stop value, indicating an unbound range. Note that if initialised like a normal range it returns a builtin `range` instance.
* `Seq`: A numeric sequence implemented as a thread safe wrapper for `itertools.count()`.
* `seq`: Return a new sequential value.
* `skip_map`: A version of `map()` which will skip items where `func(item)` raises an exception in `except_types`, a tuple of exception types. If a skipped exception occurs a warning will be issued unless `quiet` is true (default `False`).
* `splitoff`: Split a sequence into (usually short) prefixes and a tail, for example to construct subdirectory trees based on a UUID.
* `StatefulIterator`: A trivial iterator which wraps another iterator to expose some tracking state.
* `tee`: A generator yielding the items from an iterable which also copies those items to a series of queues.
* `the`: Returns the first element of an iterable, but requires there to be exactly one.
* `TrackingCounter`: A wrapper for a counter which can be incremented and decremented.
* `unrepeated`: A generator yielding items from the iterable `it` with no repetitions.

Module contents:
- <a name="ClonedIterator"></a>`class ClonedIterator(collections.abc.Iterable, typing.Generic)`: A thread safe clone of some orginal iterator.

  `next()` of this yields the next item from the supplied iterator.
  `iter()` of this returns a generator yielding from the
  historic items and then from the original iterator.

  Note that this accrues all of the items from the original
  iterator in memory.

*`ClonedIterator.__init__(self, it: Iterable)`*:
Initialise the clone with the iterable `it`.

*`ClonedIterator.__iter__(self)`*:
Iterate over the clone, returning a new iterator.

In mild violation of the iterator protocol, instead of
returning `self`, `iter(self)` returns a generator yielding
the historic and then current contents of the original iterator.

*`ClonedIterator.__next__(self)`*:
Return the next item from the original iterator.
- <a name="common_prefix_length"></a>`common_prefix_length(*seqs)`: Return the length of the common prefix of sequences `seqs`.
- <a name="common_suffix_length"></a>`common_suffix_length(*seqs)`: Return the length of the common suffix of sequences `seqs`.
- <a name="first"></a>`first(iterable)`: Return the first item from an iterable; raise `IndexError` on empty iterables.
- <a name="get0"></a>`get0(iterable, default=None)`: Return first element of an iterable, or the default.
- <a name="greedy"></a>`greedy(g=None, queue_depth=0)`: A decorator or function for greedy computation of iterables.

  If `g` is omitted or callable
  this is a decorator for a generator function
  causing it to compute greedily,
  capacity limited by `queue_depth`.

  If `g` is iterable
  this function dispatches it in a `Thread` to compute greedily,
  capacity limited by `queue_depth`.

  Example with an iterable:

      for packet in greedy(parse_data_stream(stream)):
          ... process packet ...

  which does some readahead of the stream.

  Example as a function decorator:

      @greedy
      def g(n):
          for item in range(n):
              yield n

  This can also be used directly on an existing iterable:

      for item in greedy(range(n)):
          yield n

  Normally a generator runs on demand.
  This function dispatches a `Thread` to run the iterable
  (typically a generator)
  putting yielded values to a queue
  and returns a new generator yielding from the queue.

  The `queue_depth` parameter specifies the depth of the queue
  and therefore how many values the original generator can compute
  before blocking at the queue's capacity.

  The default `queue_depth` is `0` which creates a `Channel`
  as the queue - a zero storage buffer - which lets the generator
  compute only a single value ahead of time.

  A larger `queue_depth` allocates a `Queue` with that much storage
  allowing the generator to compute as many as `queue_depth+1` values
  ahead of time.

  Here's a comparison of the behaviour:

  Example without `@greedy`
  where the "yield 1" step does not occur until after the "got 0":

      >>> from time import sleep
      >>> def g():
      ...   for i in range(2):
      ...     print("yield", i)
      ...     yield i
      ...   print("g done")
      ...
      >>> G = g(); sleep(0.1)
      >>> for i in G:
      ...   print("got", i)
      ...   sleep(0.1)
      ...
      yield 0
      got 0
      yield 1
      got 1
      g done

  Example with `@greedy`
  where the "yield 1" step computes before the "got 0":

      >>> from time import sleep
      >>> @greedy
      ... def g():
      ...   for i in range(2):
      ...     print("yield", i)
      ...     yield i
      ...   print("g done")
      ...
      >>> G = g(); sleep(0.1)
      yield 0
      >>> for i in G:
      ...   print("got", repr(i))
      ...   sleep(0.1)
      ...
      yield 1
      got 0
      g done
      got 1

  Example with `@greedy(queue_depth=1)`
  where the "yield 1" step computes before the "got 0":

      >>> from cs.x import X
      >>> from time import sleep
      >>> @greedy
      ... def g():
      ...   for i in range(3):
      ...     X("Y")
      ...     print("yield", i)
      ...     yield i
      ...   print("g done")
      ...
      >>> G = g(); sleep(2)
      yield 0
      yield 1
      >>> for i in G:
      ...   print("got", repr(i))
      ...   sleep(0.1)
      ...
      yield 2
      got 0
      yield 3
      got 1
      g done
      got 2
- <a name="imerge"></a>`imerge(*iters, **kw)`: Merge an iterable of ordered iterables in order.

  Parameters:
  * `iters`: an iterable of iterators
  * `reverse`: keyword parameter: if true, yield items in reverse order.
    This requires the iterables themselves to also be in
    reversed order.

  This function relies on the source iterables being ordered
  and their elements being comparable, through slightly misordered
  iterables (for example, as extracted from web server logs)
  will produce only slightly misordered results, as the merging
  is done on the basis of the front elements of each iterable.
- <a name="infill"></a>`infill(objs: Iterable[~_infill_T], *, obj_keys: Callable[[~_infill_T], ~_infill_K], existing_keys: Callable[[~_infill_T], ~_infill_K], all: Optional[bool] = False) -> Iterable[Tuple[~_infill_T, ~_infill_K]]`: A generator accepting an iterable of objects
  which yields `(obj,missing_keys)` 2-tuples
  indicating missing records requiring infill for each object.

  Parameters:
  * `objs`: an iterable of objects
  * `obj_keys`: a callable accepting an object and returning
    an iterable of the expected keys
  * `existsing_keys`: a callable accepting an object and returning
    an iterable of the existing keys
  * `all`: optional flag, default `False`: if true then yield
    `(obj,())` for objects with no missing records

  Example:

      for obj, missing_key in infill(objs,...):
        ... infill a record for missing_key ...
- <a name="infill_from_batches"></a>`infill_from_batches(objss: Iterable[Iterable[~_infill_T]], *, obj_keys: Callable[[~_infill_T], ~_infill_K], existing_keys: Callable[[~_infill_T], ~_infill_K], all: Optional[bool] = False, amend_batch: Optional[Callable[[Iterable[~_infill_T]], Iterable[~_infill_T]]] = <function <lambda> at 0x10dd61120>)`: A batched version of `infill(objs)` accepting an iterable of
  batches of objects which yields `(obj,obj_key)` 2-tuples
  indicating missing records requiring infill for each object.

  This is aimed at processing batches of objects where it is
  more efficient to prepare each batch as a whole, such as a
  Django `QuerySet` which lets the caller make single database
  queries for a batch of `Model` instances.
  Thus this function can be used with `cs.djutils.model_batches_qs`
  for more efficient infill processing.

  Parameters:
  * `objss`: an iterable of iterables of objects
  * `obj_keys`: a callable accepting an object and returning
    an iterable of the expected keys
  * `existsing_keys`: a callable accepting an object and returning
    an iterable of the existing keys
  * `all`: optional flag, default `False`: if true then yield
    `(obj,())` for objects with no missing records
  * `amend_batch`: optional callable to amend the batch of objects,
    for example to amend a `QuerySet` with `.select_related()` or similar
- <a name="isordered"></a>`isordered(items, reverse=False, strict=False)`: Test whether an iterable is ordered.
  Note that the iterable is iterated, so this is a destructive
  test for nonsequences.
- <a name="last"></a>`last(iterable)`: Return the last item from an iterable; raise `IndexError` on empty iterables.
- <a name="not_none"></a>`not_none(*iterables)`: Filter the iterables for items which are not `None`.
- <a name="onetomany"></a>`onetomany(func)`: A decorator for a method of a sequence to merge the results of
  passing every element of the sequence to the function, expecting
  multiple values back.

  Example:

        class X(list):
              @onetomany
              def chars(self, item):
                    return item
        strs = X(['Abc', 'Def'])
        all_chars = X.chars()
- <a name="onetoone"></a>`onetoone(func)`: A decorator for a method of a sequence to merge the results of
  passing every element of the sequence to the function, expecting a
  single value back.

  Example:

        class X(list):
              @onetoone
              def lower(self, item):
                    return item.lower()
        strs = X(['Abc', 'Def'])
        lower_strs = X.lower()
- <a name="range"></a>`class range`: A class like the builtin `range` exceppt that it will
  accept `...` as the stop value, indicating an unbound range.
  Note that if initialised like a normal range it returns a
  builtin `range` instance.

  Examples:

  Normal instantiation returns a builin `range`:

      >>> r = range(9)
      >>> type(r)
      <class 'range'>
      >>> r
      range(0, 9)

  The basic unbound range:

      >>> r0 = range(...)
      >>> type(r0)
      <class 'cs.seq.range'>
      >>> r0
      range(0:...:1)
      >>> str(r0)
      '0...'
      >>> list(r0[:10])
      [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
      >>> 99999999999999999 in r0
      True
      >>> -10 in r0
      False

  An unbound instantiation starting at 9:

      >>> r = range(9,...)
      >>> type(r)
      <class 'cs.seq.range'>
      >>> r
      range(9:...:1)
      >>> r[:10]
      range(9, 19)
      >>> r2 = r[:10]
      >>> type(r2)
      <class 'range'>
      >>> r2
      range(9, 19)
- <a name="Seq"></a>`class Seq`: A numeric sequence implemented as a thread safe wrapper for
  `itertools.count()`.

  A `Seq` is iterable and both iterating and calling it return
  the next number in the sequence.
- <a name="seq"></a>`seq()`: Return a new sequential value.
- <a name="skip_map"></a>`skip_map(func, *iterables, except_types, quiet=False)`: A version of `map()` which will skip items where `func(item)`
  raises an exception in `except_types`, a tuple of exception types.
  If a skipped exception occurs a warning will be issued unless
  `quiet` is true (default `False`).
- <a name="splitoff"></a>`splitoff(sq, *sizes)`: Split a sequence into (usually short) prefixes and a tail,
  for example to construct subdirectory trees based on a UUID.

  Example:

      >>> from uuid import UUID
      >>> uuid = 'd6d9c510-785c-468c-9aa4-b7bda343fb79'
      >>> uu = UUID(uuid).hex
      >>> uu
      'd6d9c510785c468c9aa4b7bda343fb79'
      >>> splitoff(uu, 2, 2)
      ['d6', 'd9', 'c510785c468c9aa4b7bda343fb79']
- <a name="StatefulIterator"></a>`class StatefulIterator`: A trivial iterator which wraps another iterator to expose some tracking state.

  This has 2 attributes:
  * `.it`: the internal iterator which should yield `(item,new_state)`
  * `.state`: the last state value from the internal iterator

  The originating use case is resuse of an iterator by independent
  calls that are typically sequential, specificly the `.read`
  method of file like objects. Naive sequential reads require
  the underlying storage to locate the data on every call, even
  though the previous call has just performed this task for the
  previous read. Saving the iterator used from the preceeding
  call allows the iterator to pick up directly if the file
  offset hasn't been modified in the meantime.
- <a name="tee"></a>`tee(iterable, *Qs)`: A generator yielding the items from an iterable
  which also copies those items to a series of queues.

  Parameters:
  * `iterable`: the iterable to copy
  * `Qs`: the queues, objects accepting a `.put` method.

  Note: the item is `.put` onto every queue
  before being yielded from this generator.
- <a name="the"></a>`the(iterable, context=None)`: Returns the first element of an iterable, but requires there to be
  exactly one.
- <a name="TrackingCounter"></a>`class TrackingCounter`: A wrapper for a counter which can be incremented and decremented.

  A facility is provided to wait for the counter to reach a specific value.
  The .inc and .dec methods also accept a `tag` argument to keep
  individual counts based on the tag to aid debugging.

  TODO: add `strict` option to error and abort if any counter tries
  to go below zero.

*`TrackingCounter.__init__(self, value=0, name=None, lock=None)`*:
Initialise the counter to `value` (default 0) with the optional `name`.

*`TrackingCounter.check(self)`*:
Internal consistency check.

*`TrackingCounter.dec(self, tag=None)`*:
Decrement the counter.
Wake up any threads waiting for its new value.

*`TrackingCounter.inc(self, tag=None)`*:
Increment the counter.
Wake up any threads waiting for its new value.

*`TrackingCounter.wait(self, value)`*:
Wait for the counter to reach the specified `value`.
- <a name="unrepeated"></a>`unrepeated(it, seen=None, signature=None)`: A generator yielding items from the iterable `it` with no repetitions.

  Parameters:
  * `it`: the iterable to process
  * `seen`: an optional setlike container supporting `in` and `.add()`
  * `signature`: an optional signature function for items from `it`
    which produces the value to compare to recognise repeated items;
    its values are stored in the `seen` set

  The default `signature` function is equality;
  the items are stored n `seen` and compared.
  This requires the items to be hashable and support equality tests.
  The same applies to whatever values the `signature` function produces.

  Another common signature is identity: `id`, useful for
  traversing a graph which may have cycles.

  Since `seen` accrues all the signature values for yielded items
  generally it will grow monotonicly as iteration proceeeds.
  If the items are complex or large it is well worth providing a signature
  function even if the items themselves can be used in a set.

# Release Log



*Release 20251231.1*:
range: support range[type] returning a GenericAlias.

*Release 20251231*:
range: support making a range like range[1::2] for the odd numbers.

*Release 20251230*:
* New not_none(*iterables) generator yielding items which are not none, handy in * expansions.
* New range() class accepting ... for the stop.

*Release 20250914*:
ClonedIterator: it may be an Iterable, not just an Iterator.

*Release 20250801*:
ClonedIterator: bugfix direct iteration, noticed by @Matiss.

*Release 20250724*:
New ClonedIterator class to provide a reiterable clone of an iterator.

*Release 20250306*:
New infill() and infill_from_batches() generators for identifying missing records requiring an infill.

*Release 20250103*:
New skip_map(func, *iterables, except_types, quiet=False) generator function, like map() but skipping certain exceptions.

*Release 20221118*:
Small doc improvement.

*Release 20220530*:
Seq: calling a Seq is like next(seq).

*Release 20210924*:
New greedy(iterable) or @greedy(generator_function) to let generators precompute.

*Release 20210913*:
New unrepeated() generator removing duplicates from an iterable.

*Release 20201025*:
New splitoff() function to split a sequence into (usually short) prefixes and a tail.

*Release 20200914*:
New common_prefix_length and common_suffix_length for comparing prefixes and suffixes of sequences.

*Release 20190103*:
Documentation update.

*Release 20190101*:
* New and UNTESTED class StatefulIterator to associate some externally visible state with an iterator.
* Seq: accept optional `lock` parameter.

*Release 20171231*:
* Python 2 backport for imerge().
* New tee function to duplicate an iterable to queues.
* Function isordered() is now a test instead of an assertion.
* Drop NamedTuple, NamedTupleClassFactory (unused).

*Release 20160918*:
* New function isordered() to test ordering of a sequence.
* imerge: accept new `reverse` parameter for merging reversed iterables.

*Release 20160828*:
Modify DISTINFO to say "install_requires", fixes pypi requirements.

*Release 20160827*:
TrackingCounter: accept presupplied lock object. Python 3 exec fix.

*Release 20150118*:
metadata update

*Release 20150111*:
Initial PyPI release.