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Partial application of functions and method names, supporting placeholder values for positional arguments.

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Partial application of functions and method names, supporting placeholder values for positional arguments.

Unlike functools.partial(), placeholder values are supported so that positional arguments for partial application do not need to be supplied solely from left to right. Keyword arguments are handled equivalently to functools.partial(). It is also possible to “partially apply” a method name, producing a function which looks up the method to call on the object supplied as its first argument.


  • Python 2.7 or 3.4+.


  • $ pip install partial-apply


  • Sphinx generated API documentation is available in the docs subdirectory of this repository and is also published on GitHub Pages.


An example of placeholder use:

from partial_apply import Empty, PartialFn, PartialMethod

isint = PartialFn(isinstance, Empty, int)

This makes a function isint() that takes one positional argument and returns True if it is an int and False otherwise. That is, calling isint(1) is equivalent to calling isinstance(1, int). The supplied positional arguments fill in Empty placeholder slots from left to right before reverting to functools.partial()-style appending.

An example of PartialMethod use:

count_true = PartialMethod('count', True)
count_true((False, True))  # returns 1
count_true([False, True])  # returns 1

This makes a function count_true() that counts the number of True values in a sequence. It looks up the sequence method count on the first argument and calls it with the single argument True. The calls shown are equivalent to (False, True).count(True) and [False, True].count(True). Since count_true() only stores the method name and not the method itself, it works on any type with a count() method.

Like PartialFn, PartialMethod supports placeholder positional arguments and functools.partial()-like keyword arguments.

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