FileHandles

Crossflow FileHandles

Command line tools typically take file names as arguments:

executable -i input.dat -o output.dat

This has issues if you want to do the computing on a distributed system where there is no shared filesystem. Crossflow FileHandles wrap data files as serialisable Python objects that can be safely passed around a network. Crossflow Tasks and Clients natively understand these as the equivalents of the filenames one would use for the equivalent command line call.

In normal use, FileHandles are created automatically by Tasks and/or Clients as required, the user just has to extract the required data from FileHandles returned by Tasks/Clients.

So for example, in:

output_future = client.submit(my_task, 'input.dat')
output = output_future.result()

input.dat - the name of a local file - is converted by the client into a FileHandle before being sent for processing, and output is a FileHandle which the user will (probably) want to convert back to a conventional file, using one of the methods a FileHandle provides.

Methods of crossflow.FileHandles

The .save() method of a crossflow.FileHandle creates a conventional local file with the object's contents:

output.save('output.txt')

In addition, crossflow.FileHandles follow a limited subset of the pathlib.Path API. The file handles themselves are 'path-like' and can be used in place of paths in many circumstances, e.g.:

with open(output) as f:
    data = f.read()

If your 3rd-party Python library is more picky (e.g. expects paths to be strings), then you can use the idiom:

result = my_fussy_function(str(output))

In a Path-like manner, FileHandles have .read_binary() and .read_text() methods, e.g.:

print(output.read_text()) # prints the contents of output to the screen

For more details on FileHandles, see here

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