Matching for process.extract and fuzz.ratio produce different results

[gunthercox]

Hi, I have a test case that I would like to ask about. It appears that two versions of what I believe to be logically equivalent code are returning different results.

First, this is the test data that I am using for both cases. I have a unicode string string and a list of unicode strings collection. Note that string is equal to collection[1].

string = u'⊂ ⊃ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ⊄ ⊅ ⫅ ⫆ ⫋ ⫌ ⫃ ⫄ ⫇ ⫈ ⫉ ⫊ ⟃ ⟄'

collection = [
    u'¶ ∑ ∞ ∫ π ∈ ℝ² ∖ ⩆ ⩇ ⩈ ⩉ ⩊ ⩋ ⪽ ⪾ ⪿ ⫀ ⫁ ⫂ ⋒ ⋓',
    u'⊂ ⊃ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ⊄ ⊅ ⫅ ⫆ ⫋ ⫌ ⫃ ⫄ ⫇ ⫈ ⫉ ⫊ ⟃ ⟄',
    u'∠ ∡ ⦛ ⦞ ⦟ ⦢ ⦣ ⦤ ⦥ ⦦ ⦧ ⦨ ⦩ ⦪ ⦫ ⦬ ⦭ ⦮ ⦯ ⦓ ⦔ ⦕ ⦖ ⟀',
    u'∫ ∬ ∭ ∮ ∯ ∰ ∱ ∲ ∳ ⨋ ⨌ ⨍ ⨎ ⨏ ⨐ ⨑ ⨒ ⨓ ⨔ ⨕ ⨖ ⨗ ⨘ ⨙ ⨚ ⨛ ⨜',
    u'≁ ≂ ≃ ≄ ⋍ ≅ ≆ ≇ ≈ ≉ ≊ ≋ ≌ ⩯ ⩰ ⫏ ⫐ ⫑ ⫒ ⫓ ⫔ ⫕ ⫖',
    u'¬ ⫬ ⫭ ⊨ ⊭ ∀ ∁ ∃ ∄ ∴ ∵ ⊦ ⊬ ⊧ ⊩ ⊮ ⊫ ⊯ ⊪ ⊰ ⊱ ⫗ ⫘',
    u'∧ ∨ ⊻ ⊼ ⊽ ⋎ ⋏ ⟑ ⟇ ⩑ ⩒ ⩓ ⩔ ⩕ ⩖ ⩗ ⩘ ⩙ ⩚ ⩛ ⩜ ⩝ ⩞ ⩟ ⩠ ⩢',
]

---

For my first test, I will use the extractOne method to try to find the closest match in the list.

# -*- coding: utf-8 -*-
from fuzzywuzzy import process

closest_match, ratio = process.extractOne(
    string,
    collection
)

print closest_match, ratio

This returns the string from collection[0] with a 0 as the matching ratio. This does not appear to be correct because collection[1] is an exact match to the input.

>>> ¶ ∑ ∞ ∫ π ∈ ℝ² ∖ ⩆ ⩇ ⩈ ⩉ ⩊ ⩋ ⪽ ⪾ ⪿ ⫀ ⫁ ⫂ ⋒ ⋓ 0

---

For my second test, I use fuzz and a for loop to find the closest match.

# -*- coding: utf-8 -*-
from fuzzywuzzy import fuzz

max_ratio = -1
closest_match = None

for item in collection:
    ratio = fuzz.ratio(string, item)

    if ratio > max_ratio:
        max_ratio = ratio
        closest_match = item

print closest_match, max_ratio

This returns the correct matching statement and a match ratio of 100. This seems like the correct behavior.

>>> ⊂ ⊃ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ⊄ ⊅ ⫅ ⫆ ⫋ ⫌ ⫃ ⫄ ⫇ ⫈ ⫉ ⫊ ⟃ ⟄ 100

---

So, am I misunderstanding the purpose of the process.extract methods, or is there an intentional design difference between how these two methods select a result?

Notes:

• This behavior is happening consistently in both Python 2.7, 3.4 and 3.5
• I believe this may be related to extractOne is not giving the best result #122

[DavidCEllis]

The issue is process.extract runs using fuzz.WRatio. In turn WRatio runs utils.full_process on both query and on the items in collection which turns your unicode string into an empty string. By design empty string comparisons return 0.

In[2]: from fuzzywuzzy import process, fuzz, utils
In[3]: utils.full_process(u'⊂ ⊃ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ⊄ ⊅ ⫅ ⫆ ⫋ ⫌ ⫃ ⫄ ⫇ ⫈ ⫉ ⫊ ⟃ ⟄')
Out[3]: 
''

Interestingly the first item in your list is the only item that full_process does not turn into the empty string. This leads to an interesting issue if you use a different scorer.

In[15]: process.extract(string, collection, scorer=fuzz.ratio, limit=10)
Out[15]: 

[('¶ ∑ ∞ ∫ π ∈ ℝ² ∖ ⩆ ⩇ ⩈ ⩉ ⩊ ⩋ ⪽ ⪾ ⪿ ⫀ ⫁ ⫂ ⋒ ⋓', 12),
 ('⊂ ⊃ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ⊄ ⊅ ⫅ ⫆ ⫋ ⫌ ⫃ ⫄ ⫇ ⫈ ⫉ ⫊ ⟃ ⟄', 0),
 ('∠ ∡ ⦛ ⦞ ⦟ ⦢ ⦣ ⦤ ⦥ ⦦ ⦧ ⦨ ⦩ ⦪ ⦫ ⦬ ⦭ ⦮ ⦯ ⦓ ⦔ ⦕ ⦖ ⟀', 0),
 ('∫ ∬ ∭ ∮ ∯ ∰ ∱ ∲ ∳ ⨋ ⨌ ⨍ ⨎ ⨏ ⨐ ⨑ ⨒ ⨓ ⨔ ⨕ ⨖ ⨗ ⨘ ⨙ ⨚ ⨛ ⨜', 0),
 ('≁ ≂ ≃ ≄ ⋍ ≅ ≆ ≇ ≈ ≉ ≊ ≋ ≌ ⩯ ⩰ ⫏ ⫐ ⫑ ⫒ ⫓ ⫔ ⫕ ⫖', 0),
 ('¬ ⫬ ⫭ ⊨ ⊭ ∀ ∁ ∃ ∄ ∴ ∵ ⊦ ⊬ ⊧ ⊩ ⊮ ⊫ ⊯ ⊪ ⊰ ⊱ ⫗ ⫘', 0),
 ('∧ ∨ ⊻ ⊼ ⊽ ⋎ ⋏ ⟑ ⟇ ⩑ ⩒ ⩓ ⩔ ⩕ ⩖ ⩗ ⩘ ⩙ ⩚ ⩛ ⩜ ⩝ ⩞ ⩟ ⩠ ⩢', 0)]

This occurs because process.extract is still running this full_process on the 'choices' but also it's not running it on the 'query' (I think this is a bug and will submit it shortly).

If you did want to use process.extract the method would be to bypass this full_process. Luckily you can do this.

In[18]: process.extract(string, collection, scorer=fuzz.ratio, processor=lambda x: x, limit=10)
Out[18]: 

[('⊂ ⊃ ⊆ ⊇ ⊈ ⊉ ⊊ ⊋ ⊄ ⊅ ⫅ ⫆ ⫋ ⫌ ⫃ ⫄ ⫇ ⫈ ⫉ ⫊ ⟃ ⟄', 100),
 ('¶ ∑ ∞ ∫ π ∈ ℝ² ∖ ⩆ ⩇ ⩈ ⩉ ⩊ ⩋ ⪽ ⪾ ⪿ ⫀ ⫁ ⫂ ⋒ ⋓', 48),
 ('≁ ≂ ≃ ≄ ⋍ ≅ ≆ ≇ ≈ ≉ ≊ ≋ ≌ ⩯ ⩰ ⫏ ⫐ ⫑ ⫒ ⫓ ⫔ ⫕ ⫖', 48),
 ('¬ ⫬ ⫭ ⊨ ⊭ ∀ ∁ ∃ ∄ ∴ ∵ ⊦ ⊬ ⊧ ⊩ ⊮ ⊫ ⊯ ⊪ ⊰ ⊱ ⫗ ⫘', 48),
 ('∠ ∡ ⦛ ⦞ ⦟ ⦢ ⦣ ⦤ ⦥ ⦦ ⦧ ⦨ ⦩ ⦪ ⦫ ⦬ ⦭ ⦮ ⦯ ⦓ ⦔ ⦕ ⦖ ⟀', 47),
 ('∧ ∨ ⊻ ⊼ ⊽ ⋎ ⋏ ⟑ ⟇ ⩑ ⩒ ⩓ ⩔ ⩕ ⩖ ⩗ ⩘ ⩙ ⩚ ⩛ ⩜ ⩝ ⩞ ⩟ ⩠ ⩢', 45),
 ('∫ ∬ ∭ ∮ ∯ ∰ ∱ ∲ ∳ ⨋ ⨌ ⨍ ⨎ ⨏ ⨐ ⨑ ⨒ ⨓ ⨔ ⨕ ⨖ ⨗ ⨘ ⨙ ⨚ ⨛ ⨜', 44)]

Which correctly gives your full string as the 100% match.