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Python 3: An interactive deep dive

A List Of Functions

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Now you’re going to add a level of abstraction. You started by defining a list of rules: if this, do that, otherwise go to the next rule. Let’s temporarily complicate part of the program so you can simplify another part.

Python 3.5
import re
def match_sxz(noun):
    return re.search('[sxz]$', noun)
def apply_sxz(noun):
    return re.sub('$', 'es', noun)
def match_h(noun):
    return re.search('[^aeioudgkprt]h$', noun)
def apply_h(noun):
    return re.sub('$', 'es', noun)
def match_y(noun):                             #①
    return re.search('[^aeiou]y$', noun)
        
def apply_y(noun):                             #②
    return re.sub('y$', 'ies', noun)
def match_default(noun):
    return True
def apply_default(noun):
    return noun + 's'
rules = ((match_sxz, apply_sxz),               #③
         (match_h, apply_h),
         (match_y, apply_y),
         (match_default, apply_default)
         )
def plural(noun):           
    for matches_rule, apply_rule in rules:       #④
        if matches_rule(noun):
            return apply_rule(noun)

① Now, each match rule is its own function which returns the results of calling the re.search() function.

② Each apply rule is also its own function which calls the re.sub() function to apply the appropriate pluralization rule.

③ Instead of having one function (plural()) with multiple rules, you have the rules data structure, which is a sequence of pairs of functions.

④ Since the rules have been ...