================== Parallel execution

The parallel verb family runs a callable over a batch of items -- on threads, processes, or asyncio -- with a progress bar. The how-to guide (:doc:../howto/parallel-execution) shows the idioms; this page is the API reference.

The shared keywords

Every verb accepts (where applicable):

.. list-table:: :header-rows: 1 :widths: 22 78

• • Keyword
  • What it does
• • workers
  • Pool size for the sync verbs. Default: the executor's own default (min(32, cpus + 4) threads, cpus processes). Accepted as an alias for concurrency on the async verbs.
• • concurrency
  • Async verbs: maximum in-flight tasks. None (default) creates every task up front, like asyncio.gather.
• • pool
  • 'thread' (default), 'process', 'interpreter' (Python 3.14+), or an existing :py:class:concurrent.futures.Executor instance (used as-is, never shut down for you).
• • bar
  • 'plain' (one aggregate bar, default), 'multi' (a :py:class:~progressbar.multi.MultiBar with one sub-bar per in-flight task), False (no output), or a configured ProgressBar/MultiBar instance to drive.
• • on_error
  • 'raise' (default): first failure cancels pending work and re-raises. 'return': exceptions appear in place of their results; KeyboardInterrupt/SystemExit still propagate.
• • chunksize
  • Items per task. Default: 1 on threads; automatic on process and interpreter pools (about 16 chunks per worker, capped at 1000). The bar advances per chunk.
• • buffersize
  • Maximum unfinished submitted tasks (sync verbs). Default max(4 × workers, 16); keeps memory flat on huge or lazy inputs.
• • timeout
  • Overall deadline in seconds. Expiry cancels pending work and raises TimeoutError without waiting for running tasks.
• • poll_interval
  • Seconds between coordinator wakeups and no-progress bar redraws (default 0.1) -- one knob for both.
• • initializer, initargs, mp_context, max_tasks_per_child, thread_name_prefix
  • Forwarded verbatim to the executor constructor (max_tasks_per_child needs Python 3.11+; each option is validated against the pool kind).
• • **bar_kwargs
  • Anything else goes to the bar: prefix=/desc=, suffix=, widgets=, max_value=, ... Unknown names raise TypeError.

Sync verbs

.. autofunction:: progressbar.map :no-index: .. autofunction:: progressbar.imap :no-index: .. autofunction:: progressbar.imap_unordered :no-index: .. autofunction:: progressbar.starmap :no-index: .. autofunction:: progressbar.thread_map :no-index: .. autofunction:: progressbar.process_map :no-index: .. autofunction:: progressbar.as_completed :no-index: .. autofunction:: progressbar.run :no-index:

Async verbs

.. autofunction:: progressbar.amap :no-index: .. autofunction:: progressbar.aimap :no-index: .. autofunction:: progressbar.aimap_unordered :no-index: .. autofunction:: progressbar.gather :no-index:

Reusable layers

.. autoclass:: progressbar.Pool :members: :member-order: bysource :no-index:

.. autoclass:: progressbar.AsyncPool :members: :member-order: bysource :no-index:

.. autofunction:: progressbar.parallel :no-index: .. autofunction:: progressbar.current_task_bar :no-index:

.. autoclass:: progressbar.ParallelFunction :members: :no-index: