Python fill string with formats with dictionary

Question

Say I have templates to fill with values in dict:

I have templates like this:

templates = [
   "I have four {fruit} in {place}", 
   "I have four {fruit} and {grain} in {place}",
   ...
]

With dictionary like this:

my_dict = {'fruit': ['apple', 'banana', 'mango'], 
           'place': ['kitchen', 'living room'],
           'grain' : ['wheat', 'rice']
          }

Say I have a sentence like this:

sentence = "I have four apple in kitchen" 

Given this sentence, templates, and dictionary, I would like to know that sentence matched one of the templates and return values which it matched like this:

{'fruit': 'apple', 'place': 'kitchen'}

And similar to above if:

Input: "I have four apple and wheat in kitchen"
Output: {'fruit': 'apple', 'grain': 'wheat', 'place': 'kitchen'}

And it would be great if it can handle this too:

Input: "I have four apple in bedroom" 
Output: {'fruit': 'apple'}

Notice it only returns fruit and not bedroom since bedroom is not in the values of place.

Answer 1

Turn your formatted strings into regular expressions:

import re

words = {k: '(?P<{}>{})'.format(k, '|'.join(map(re.escape, v))) for k, v in my_dict.items()}
patterns = [re.compile(template.format(**words)) for template in templates]

This produces patterns of the form I have four (?P<fruit>apple|banana|mango) in (?P<place>kitchen|living room)". Matching these then provides you with your expected output:

for pattern in patterns:
    match = pattern.match(sentence)
    if match:
        matched_words = match.groupdict()

This is a very fast, O(N) approach to matching sentences exactly:

>>> import re
>>> templates = [
...    "I have four {fruit} in {place}",
...    "I have four {fruit} and {grain} in {place}",
... ]
>>> my_dict = {'fruit': ['apple', 'banana', 'mango'],
...            'place': ['kitchen', 'living room'],
...            'grain' : ['wheat', 'rice']
...           }
>>> def find_matches(sentence):
...     for pattern in patterns:
...         match = pattern.match(sentence)
...         if match:
...             return match.groupdict()
...
>>> find_matches("I have four apple in kitchen")
{'fruit': 'apple', 'place': 'kitchen'}
>>> find_matches("I have four apple and wheat in kitchen")
{'fruit': 'apple', 'grain': 'wheat', 'place': 'kitchen'}

If you need your templates to match partial sentences, wrap the optional parts in (?...) groups:

"I have four {fruit} in (?{place})"

or add \w+ to the words list (in addition to the valid words), then validate groupdict() result against my_dict after matching. For the in bedroom case, \w+ will match the bedroom part but won't be found in the my_dict list for place, for example.