dispatchonvalue 0.9.1

Python package providing dispatch on values for arbitrarily nested lists and dictionary data structures.

This package provides dispatch on value complex for arbitrarily nested lists and dictionaries. You can use lambda to do expression matching and an any_X token that is a wildcard that ensures identical values can be matched. It is useful for getting rid of complicated and difficult to read if...elif...elif... chains. The package also allows the creation of dynamic patterns.

The home page is on github at:

https://github.com/minimind/dispatch-on-value-for-python

Install using pip:

pip install dispatchonvalue

Unit tests can be run from the source directory using:

python -m unittest discover -s test

Any queries and comments are welcome and can be sent to me at:

[e-mail]

Quick guide

Start your code with this:

import dispatchonvalue as dv

dispatch_on_value = dv.DispatchOnValue()

Then register your overloaded functions:

@dispatch_on_value.add([1, 2, 3])
def _(a):
    assert a == [1, 2, 3]
    # Do something

@dispatch_on_value.add([4, 5, 6])
def _(a):
    assert a == [4, 5, 6]
    # Do something

Then later, call the correct overloaded functions:

p = [4, 5, 6]
dispatch_on_value.dispatch(p)  # Should call second function above

The return value is True or False, depending upon whether a function could be matched and called.

Some quick examples

Multiple dispatch on value

@dispatch_on_value.add([1, 2, 3])
def fn_1(a):
    assert a == [1, 2, 3]
    # Do something

@dispatch_on_value.add([4, 5, 6])
def fn_2(a):
    assert a == [4, 5, 6]
    # Do something

p = [1, 2, 3]
dispatch_on_value.dispatch(p)  # This will call fn_1 and return True

p = [4, 5, 6]
dispatch_on_value.dispatch(p)  # This will call fn_2 and return True

p = [1, 2, 6]
dispatch_on_value.dispatch(p)  # This will not call anything and return False

Data structure patterns can be arbitrary nested

@dispatch_on_value.add({'one': 3, 'animals': ['frog', 'mouse']})

Wildcards

Use of wildcard tokens any_a, any_b, … any_z that will ensure values are identical. e.g.:

@dispatch_on_value.add([dv.any_a, 'b', 3, [3, 'd', dv.any_a]])
def _(a):
    # Do something

dispatch_on_value.dispatch(['c', 'b', 3, [3, 'd', 'c']])  # This will match
dispatch_on_value.dispatch(['f', 'b', 3, [3, 'd', 'f']])  # This will match
dispatch_on_value.dispatch(['c', 'b', 3, [3, 'd', 'f']])  # This will not match

Insert Lambda for wide expression of patterns

Use lambda’s as part of the pattern matching:

@dispatch_on_value.add([1, 2, lambda x: 3 < x < 7, 'hello'])
def _(a):
    # Do something

dispatch_on_value.dispatch([1, 2, 4, 'hello'])  # This will match
dispatch_on_value.dispatch([1, 2, 2, 'hello'])  # This will not match

Another example:

@dispatch_on_value.add(['a', 2, lambda x: x == 'b' or x == 'c'])
def _(a):
    # Do something

dispatch_on_value.dispatch(['a', 2, 'c'])  # This will match
dispatch_on_value.dispatch(['a', 2, 's'])  # This will not match

No limit on parameters

You can pass as many extra parameters as you want when dispatching:

@dispatch_on_value.add([1, 2])
def _(a, my_abc, my_def):
    assert a == [1, 2]
    # Do something

dispatch_on_value.dispatch([1, 2], 'abc', 'def')

Matching on dictionaries is either partial or strict

Matching on directories is partial by default. This means dictionaries will match if all the key/value pairs in the pattern are matched - any extra pairs will be ignored. You can ensure the dictionaries are exactly the same by using dispatch_strict() rather than dispatch(). For example:

@dispatch_on_value.add({'name': 'john', 'age': 32})
def _(a):
    # Do something

# These will match because they contain the minimal dictionary items
dispatch_on_value.dispatch({'name': 'john', 'age': 32})
dispatch_on_value.dispatch({'name': 'john', 'age': 32, 'sex': 'male'})

# This will match because it's strict and the pattern is exactly the same
dispatch_on_value.dispatch_strict({'name': 'john', 'age': 32})

# This will not match because the dictionary doesn't match exactly
dispatch_on_value.dispatch_strict({'name': 'john', 'age': 32, 'sex': 'male'})