Regex to detect Python Dictionary Syntax

Question

I’ve been struggling and my head is about to explode. So I need to write a basic Regex script in Python that will identify if a string has the format (pattern) of a Python dictionary. With the code below, I’ve only managed to successfully match when the string is like this: my_dict = {1: 'apple', 2: 'ball'}

I would like to match something like the below which doesn’t only use numbers as keys and alphabets as values:

{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

—————Dictionary Detector——————-

# importing regex module
import re

# printing script purpose
# `n` is for printing newline
print('nScript designed to detect whether if user input is a Python dictionary construction.n')

# getting user input
user_inp = input('Type Text> ')

if user_inp != '{}':
    user_inp = user_inp.replace('}', ',}', 1)

if re.search('''^{((('(w|d)*')|(w|d)*) *: * (('(w|d)*')|(w|d)*) *, *)*}$''', user_inp):
    print('yes, a dictionary has been detected.')

else:
    print('No dictionary has been detected.')

Asked By: Mohammed Hoorzook

||

Source

Answer 1

As mentioned in the comments, json might be a better fit, but if you still want to do it with regex, here is one:

dict_reg = re.compile(r"""
s*                 # user might leave spaces in front
{                   # the opening curly of dict
(                   # the key-value pair groups begin
s*                 # user might leave a space
["'().,w]+        # the "key" part: matches strings, tuples, numbers and variables
s*:s*             # the colon and possible spaces around
["'()[].,w]+    # the "value" part: matches strings, tuples, lists, numbers and variables
s*                 # again, user might leave a space after writing value
,?                  # the comma that seperates key-value pairs (optional, last one may not have it)
s*                 # again, user might leave a space
)*                  # the key-value pair groups as many as possible (* implies empty dict is also ok)
}                   # the closing curly of dict
s*                 # again, user might leave a space because why not
""", re.VERBOSE)

You can use as:

re.fullmatch(dict_reg, user_inp)

The apparent cases it does not match:

arithmetic expressions e.g. 2+5 as keys or values

dicts as values

nested dicts

and possibly many more. But it should do okay for basic dictionaries.

Answered By: Mustafa Aydın

Answer 2

It’s not really a regex solution, but if you are using python, you can do:

def is_dictionary(string) -> bool:
        if type(eval(string)) is dict:
            return True
        else:
            return False

Answered By: Muszo

Regex to detect Python Dictionary Syntax

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