Less than Or Greater Than Comparison as a Variable in Python

问题

I have a block of code in a function that does some comparisons, namely:

if customer_info['total_dls'] < min_training_actions \
or customer_info['percentage'] > train_perc_cutoff:
    continue
elif customer_id not in test_set \
or test_set[customer_id]['total_dls'] < min_testing_actions:
    num_uncertain +=1
    continue
elif test_set[customer_id]['percentage'] <= test_perc_cutoff:
    num_correct +=1
else:
    num_incorrect +=1

Now sometimes I need to do those comparisons to be greater than, and sometimes I need them to be less than. All of the rest of the code is exactly the same. Now, I could just make two functions that reuse basically the same code, but before I do, is there some clean way to variabalize the comparison operator, so I could just use the same block of code and pass in the comparison as a variable? Something like: compare(var1, var2, polarity). I know I can make this myself, but I'm wondering what the standard is in cases like this. Is there some pretty pythonic way of doing this I'm unaware of?

[Edit] Adding emphasis to the most important part of the question [/Edit]

回答1:

You can use the operator module; it has functions that act as the comparison operators:

import operator

if foobar:
    comp = operator.lt
else:
    comp = operator.gt

if comp(spam, eggs):

This'll use either test if spam is less then, or greater then eggs, depending on the truth of foobar.

This fits your comparison as a variable requirement exactly.

This is certainly what I'd use to avoid repeating myself; if you have two pieces of code that differ only in the comparison direction, use a function from operators to parameterize the comparison.

回答2:

I would not refactor this by making the operators dynamic in any way. I think the comparisons aren't that similar and forcing them to look more similar obfuscates the code. It's a bit of a red herring.

I would put the complex checks in a function, something like

def customer_trained_enough(customer_info):
    return (
        customer_info['total_dls'] < min_training_actions
        or customer_info['percentage'] > train_perc_cutoff)

def customer_tested_enough(test_info):
    return test_info['total_dls'] >= min_testing_actions

def percentage_too_high(test_info):
    return test_info['percentage'] > test_perc_cutoff

And then the code becomes:

if customer_trained_enough(customer_info):
    continue
if (customer_id not in test_set or
    not customer_tested_enough(test_set[customer_id])):
    num_uncertain += 1
elif not percentage_too_high(test_set[customer_id]):
    num_correct += 1
      else:
    num_incorrect += 1

I guessed some names for the functions, and had to negate the logic in two of them to make the names work.

回答3:

I had the same question when trying to build a module for unknown ML models. Some require a minimum score to perform, others a maximum score, depending on the metric used. I passed in a 'greater than' boolean variable and wrote a small function:

def is_better(gt,a,b): 
    return a>b if gt else a<b

来源：https://stackoverflow.com/questions/23349136/less-than-or-greater-than-comparison-as-a-variable-in-python

标签

python

comparison-operators