Dryable - enabling `--dry-run` functionality

Sometimes we are want to check the basic logic of our programs without running certain operations that are lengthy and cause side effects.

E.g. we would like some script to tell us what it would have done, but without actually doing it: a good example is when you have a script that is supposed to delete some old files or database entries, and you want to use a “dry run” to see what it would do, before actually letting it loose.

$ ./my-deleting-script --dry-run # don't really delete anything, just show me

The problem with that sort of thing is that your code gets filled with annoying if statements like:

if not dryRun:
    doTheThing()
else:
    logTheThing()

This is precisely what Dryable is for. You set the “dry run” mode like this:

dryable.set( True ) # or False to turn it off

Here’s an example if how to use it:

import dryable
import requests
import sys

def findOldFilesForDeletion():
    return [ 'some', 'results' ]

@dryable.Dryable()
def deleteFiles( results ):
    print( 'will now open an real world connection'
           'that requires a server and will make side effects' )
    requests.post( 'http://url.to.some.server/results', data = str( results ) )


# the next line ensures that deleteFiles
# will not run if --dry-run is specified on the command line
dryable.set( '--dry-run' in sys.argv )

# now code as usual
results = findOldFilesForDeletion()
print( 'got: {}'.format( results ) )
deleteFiles( results )

Installation

Install dryable like so

$ pip install dryable

Returning Custom Values

By default a Dryable decorated function will return None in dry-run mode. If you need some other value, specify it like so:

@dryable.Dryable( [ 'fake person 1', 'fake person 2' ] )
def getPeopleFromDatabase():
    return actualQueryFromDB()

What If I Have Different Things I Want To Dry-Run?

If you’re using dryable, you may run into situations in which you want to dry-run some code, but not some other code. E.g. you want to have --dont-delete-files and separately --dont-save-to-db or something. The way to handle this situation is with labels

import dryable

@dryable.Dryable( label = 'labelA' )
def functionA():
    print( "Hi, I am A" )

@dryable.Dryable( label = 'labelB' )
def functionB():
    print( "Hi, I am B" )

dryable.set( True, 'labelA' )
functionA() # this will be dried up
functionB() # this will run for real

Logging

Dryable logs to a logger called dryable which is available via Dryable.logger

What If I want to log a dryable function with a custom message ?

You can define a custom message using logging_msg parameter:

import dryable

@dryable.Dryable( logging_msg = 'Function A were not executed (--dry-run)' )
def functionA():
    print( "Hi, I am A" )

Optionally, you may also inject the following patterns, which will be interpreted by Dryable:

Placeholder	Description
`{label}`	Label defined in `@Dryable()`
`{function}`	Function name
`{args}`, `{kwargs}`	Args and kwargs passed to the function

import dryable

@dryable.Dryable( logging_msg = 'Would have called {function} with args {args} (--dry-run)' )
def functionA(paramA):
    print( "Hi, I am A" )

Dryable - enabling --dry-run functionality