Joblib: running Python function as pipeline jobs
Joblib is a set of tools to provide lightweight pipelining in
Python. In particular, joblib offers:
- transparent disk-caching of the output values and lazy re-evaluation
- easy simple parallel computing
- logging and tracing of the execution
Joblib is optimized to be fast and robust in particular on large
data and has specific optimizations for numpy arrays. It is
The vision is to provide tools to easily achieve better performance and
reproducibility when working with long running jobs.
- Avoid computing twice the same thing: code is rerun over an
over, for instance when prototyping computational-heavy jobs (as in
scientific development), but hand-crafted solution to alleviate this
issue is error-prone and often leads to unreproducible results
- Persist to disk transparently: persisting in an efficient way
arbitrary objects containing large data is hard. Using
joblib’s caching mechanism avoids hand-written persistence and
implicitly links the file on disk to the execution context of
the original Python object. As a result, joblib’s persistence is
good for resuming an application status or computational job, eg
after a crash.
Joblib strives to address these problems while leaving your code and
your flow control as unmodified as possible (no framework, no new
Transparent and fast disk-caching of output value: a memoize or
make-like functionality for Python functions that works well for
arbitrary Python objects, including very large numpy arrays. Separate
persistence and flow-execution logic from domain logic or algorithmic
code by writing the operations as a set of steps with well-defined
inputs and outputs: Python functions. Joblib can save their
computation to disk and rerun it only if necessary:
>>> import numpy as np
>>> from joblib import Memory
>>> mem = Memory(cachedir='/tmp/joblib')
>>> import numpy as np
>>> a = np.vander(np.arange(3)).astype(np.float)
>>> square = mem.cache(np.square)
>>> b = square(a)
[Memory] Calling square...
square(array([[ 0., 0., 1.],
[ 1., 1., 1.],
[ 4., 2., 1.]]))
___________________________________________________________square - 0...s, 0.0min
>>> c = square(a)
>>> # The above call did not trigger an evaluation
Embarrassingly parallel helper: to make is easy to write readable
parallel code and debug it quickly:
>>> from joblib import Parallel, delayed
>>> from math import sqrt
>>> Parallel(n_jobs=1)(delayed(sqrt)(i**2) for i in range(10))
[0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0]
Logging/tracing: The different functionalities will
progressively acquire better logging mechanism to help track what
has been ran, and capture I/O easily. In addition, Joblib will
provide a few I/O primitives, to easily define define logging and
display streams, and provide a way of compiling a report.
We want to be able to quickly inspect what has been run.
Fast compressed Persistence: a replacement for pickle to work
efficiently on Python objects containing large data (
joblib.dump & joblib.load ).
||A context object for caching a function’s return value each time it is called with the same input arguments.
||Helper class for readable parallel mapping.
|dump (value, filename[, compress, cache_size])
||Fast persistence of an arbitrary Python object into a files, with dedicated storage for numpy arrays.
|load (filename[, mmap_mode])
||Reconstruct a Python object from a file persisted with joblib.load.
|hash (obj[, hash_name, coerce_mmap])
||Quick calculation of a hash to identify uniquely Python objects containing numpy arrays.