How to add space to both ends of a equal-sign when not in parentheses with specified file types? - sublimetext2

Question

Is it possible? For example, When in .py and .lua file, not in () and I type =, st3 will automatically add a space to both ends. such as a assignment statement:
a = 1
But it is disabled if in a () state:
func(a=1)
func(a=1,func(b=1))

Answer 1

You can do this by creating a keybinding on the = key, to insert a space, followed by the = and another space, that will check:
that the syntax at the caret corresponds to Python or Lua
that the text between the beginning of the line and the text caret contains no unbalanced brackets
If the conditions are not met, the keybinding is not used, and = will be inserted without surrounding whitespace as normal. (Assuming other keybindings on the = key, if any, are evaluated and found not to apply.)
Steps
In Sublime Text, open the Preferences menu and select Keybindings - User.
If the document is not empty, move the text caret to after the first [ character at the beginning of the document.
Paste in the following:
{ "keys": ["="], "command": "insert", "args": { "characters": " = " }, "context":
[
{ "key": "selection_empty", "operator": "equal", "operand": true, "match_all": true },
{ "key": "selector", "operator": "equal", "operand": "source.python, source.lua", "match_all": true },
{ "key": "preceding_text", "operator": "regex_match", "operand": "^(([^()]*+)(\\((?:(?2)|(?3))*\\))?+)(?1)*+$", "match_all": true }
]
},
If the document was previously empty, type a [ at the beginning of the document, and a ] at the end of the document. This is to ensure that it is a valid JSON array.
Save the file.
Press the = key in a Python or Lua document, and see that it will automatically insert spaces around it when not inside unbalanced parens.
Explanation of the regex:
This aspect of Sublime Text uses the PCRE regex flavor provided by the Boost library, which supports recursion, and thus allows us to not have to repeat ourselves to determine whether the brackets are balanced or not.
^ start of the line
( begin capture group 1
([^()]*+) - possessively capture every consecutive non-parenthesis character into capture group 2
( begin capture group 3
\( match a literal ( character
(?:(?2)|(?3))* recursively match the same regex pattern that corresponds to capture group 2 or 3 (i.e. recursive), zero or unlimited times
\) match a literal ) character
) end capture group 3
?+ make the previous group optional but possessive
) end capture group 1
(?1)*+ possessively recursively match the same regex pattern that corresponds to capture group 1, zero or unlimited times
$ end of the text to be matched - in this case, where the text caret is, because the preceding_text context is used.
The overall effect is that is will match where any of the following are true on the line where the text caret is, before the caret position:
no parens are used
non-nested parens are opened and closed
nested parens are all closed
there are no closing parens that don't have a corresponding open paren
Because the regex is being stored in JSON, the \ characters need to be escaped with an extra \, which is why the operand string contains \\( but I only refer to \( in the regex explanation.
Scope Selector
To ensure that the keybinding is only active on Python and lua, the scope selector context is used, with an argument of source.python, source.lua. This selector matches either source.python or source.lua, or indeed both together if such a thing were possible to embed one language in the other.
One way to find what the base scope of a language in Sublime Text is, would be to go to the very beginning of a document set to the relevant syntax, and go to the Tools menu -> Developer -> Show Scope Name. It will even work on an empty file.
Scope selectors are borrowed from TextMate, and more documentation on them can be found here:
TextMate docs
SO answer
Keybinding Documentation
More information about keybindings can be found here: http://docs.sublimetext.info/en/latest/reference/key_bindings.html#structure-of-a-key-binding
I personally find it useful to view the default keybindings for inspiration.