3203：Incremental Python Parsing

For the sake of simplicity, only the following subset of Python syntax is considered:

PLAIN_TEXT:
    [^"()\[\]{}]+
STRING:
    \"[^"]*\"
text:
      (empty)
    | text PLAIN_TEXT
    | text STRING
    | text bracket_enclosed_text
bracket_enclosed_text:
      ( text )
    | [ text ]
    | { text }

From the syntax some terms are defined as follows:

1. String: a sequence delimited by quotes (") of characters other than quotes, possibly including new-lines.

   Examples:
     "a(bc"
  "a
bc)"
  "usage: foo [bar]
this help information
is
totally
useless"

   (Python actually """ for such strings, but let’s accept the modification just for this problem.)

2. Bracket-enclosed text: a sequence of characters other than brackets or quotes enclosed by matched pairs of brackets.

   Example:
     (1)
  {a->[foo.bar(
  "a[",b,c
  )]}

3. Logical new-line: a new-line character that is not part of a string or bracket-enclosed text

4. Physical line: a maximal sequence of characters other than new-line characters

   Examples:
   def a(b)    # physical line 1
  foo.bar(  # physical line 2
  "a[",b)   # physical line 3
"blah blah, # physical line 4
blah"       # physical line 5

5. Logical line: a maximal sequence of characters other than logical new-lines

   Examples:
   def a(b)    # logical line 1
  foo.bar(  # logical line 2
  "a[",b)   # logical line 2
"blah blah, # logical line 3
blah"       # logical line 3 

6. Valid/invalid program: a program without/with mismatched quotes or brackets that are not part of any strings 

   Examples:
     def a(b
  "blah

Given a program, you are to implement the following primitive operations:

• modify(a, b, c): Modify the character at physical line a, column b to c
• query(a, b): Tell which logical line the character at physical line a, column b is on.