Usage

To use Parallel TQDM in a project:

import pqdm

There very basic usage is running pqdm on an Iterable whose elements are directly supported by the Callable passed to pqdm:

from pqdm.processes import pqdm
# If you want threads instead:
# from pqdm.threads import pqdm

args = [1, 2, 3, 4, 5]
# args = range(1,6) would also work

def square(a):
    return a*a

result = pqdm(args, square, n_jobs=2)

Everytime you run pqdm with more than one job (i.e. n_jobs > 1) you will need to make a decision about the backend used, the standard options from Python’s concurrent.futures library are:

  • threads: share memory with the main process, subject to GIL, low benefit on CPU heavy tasks, best for IO tasks or tasks involving external systems,
  • processes: best for CPU heavy tasks, GIL-free, have an IO overhead due to lack of shared memory and need to dump/pickle data

With both backends pqdm supports bounded variants, which are semaphore guarded. For more information on processes vs threads see the concurent futures documentation or Brendant Fortuner’s medium post.

Different ways to pass arguments to function

By default pqdm assumes your function can handle the element taken from Iterable, you may however want to have other kinds of situations:

  • an Iterable[Dict[str, Any]] which you would like to pass as named arguments to a function,
  • or Iterable[Union[List, Tuple]] which you would like to pass as positional arguments to a function

The library supports both variants, here’s how a named argument should be passed:

from pqdm.processes import pqdm
# If you want threads instead:
# from pqdm.threads import pqdm

args = [
    {'a': 1, 'b': 2},
    {'a': 2, 'b': 3},
    {'a': 3, 'b': 4},
    {'a': 4, 'b': 5}
]
# args = range(1,6) would also work

def multiply(a, b):
    return a*b

result = pqdm(args, multiply, n_jobs=2, argument_type='kwargs')
# result is [2, 6, 12, 20]

and for the positional arguments:

from pqdm.processes import pqdm
# If you want threads instead:
# from pqdm.threads import pqdm

args = [[1, 2], [2, 3], [3, 4], [4, 5]],
# args = range(1,6) would also work

def multiply(a, b):
    return a*b

result = pqdm(args, multiply, n_jobs=2, argument_type='args')
# result is [2, 6, 12, 20]

Passing arguments to tqdm

You may want to change tqdm output, for this reason any option not handle by the Executor class from concurrent.futures is passed to tqdm.

from pqdm.processes import pqdm
# If you want threads instead:
# from pqdm.threads import pqdm

args = [1, 2, 3, 4, 5]

def square(a):
    return a*a

result = pqdm(args, square, n_jobs=2, desc='Squaring elements', unit='el')