将参数传递给变量引用的函数

Question

The Issue

I am writing a file parser for program input files that can be somewhat deconstructed to dictionaries: that is, in the input file, there are multi-level 'dicts' containing 'key-value pairs'.

I have a keywords dictionary which tells a read function which keys to read, and how to parse the key values.

For example, you can see in the code excerpt below that when datum is read, the value should be parsed with the function HelperFunctions.split_to_floats :

'datum': HelperFunctions.split_to_floats

The Goal

What I would like to do is be able to pass in arguments, such that I do not have to make function permutations for each possible type of ie value delimiter.

For example, to restructure the keywords dictionary in something like:

keywords = {
    '_root': str,
    'units': HelperFunctions._split(LINE,to=str,delim=','),
    'datum': HelperFunctions._split(LINE,to=float,delim=' ')
    }

Code Sample

A full, workable demo of what I currently have is reproduced below:

class HelperFunctions:

    def comma_split_to_strings(string:str) -> list:
        # Returns a list of strings
        return string.split(',')

    def split_to_floats(string:str) -> list:
        # Returns a 1D list of floats
        return list(map(float,string.split()))


keywords = {
    '_root': str,
    'units': HelperFunctions.comma_split_to_strings,
    'datum': HelperFunctions.split_to_floats
    }

card = {}
key = 'units'
value = 'Pa,kg,km'

if key in keywords:
    cast = keywords[key]

    card[key] = cast(value)

Answer 1

What you are looking for is partial in functools. It lets you create a function with some of parameters bound to values such that you can call the returned function later with the missing values.

from functools import partial

# Bind the parameters you want to "freeze"
keywords = {
    '_root': str,
    'units': partial(HelperFunctions._split, to=str, delim=','),
    'datum': partial(HelperFunctions._split, to=float, delim=' ')
    }

# The later you just need to provide LINE
keywords['units'](LINE)

Answer 2

Are you looking for functools.partial ?

from functools import partial

keywords = {
    '_root': str,
    'units': partial(HelperFunctions._split, to=str, delim=','),
    'datum': partial(HelperFunctions._split, to=float, delim=' ')
}