How to parse a function with ply in Python?

I'm trying to parse a custom programming language using PLY in Python, and I'm a bit confused.

For example, I want to parse:

on create:
  modifyProp relative width => 11
  modifyProp height => 14

I want to make the on part work like def and then read the next part as an input (in this case create), and then parse the : like in Python.

I also want to make the modifyProp part in the same way, with relative being read as a parameter instead of an input if it's included, and then reading => as a "change this to" command, then reading the integer.

How can I do that?

Solution

We want:

on create:
  modifyProp relative width => 11
  modifyProp height => 14

as string and formatted in Python:

some_code_in_string = '''
def create(relative):
    def modifyProp(relative):
        return True if relative[0] >= 11 and relative[1] >= 14 else False
    return modifyProp(relative)
print(create(relative))
'''

so that we can execute some_code_in_string:

exec(some_code_in_string, {'relative': [15, 20]})

Outputs:

True

Now if we have a few lines of that code already in string (which you might already have as a file), we can do something like:

def pythonicize(some_string):
    some_new_string = ''
    func_end = some_string.find(':')
    func_start = True
    index = func_end - 1
    while not some_string[index:func_end].__contains__(' '):
        index -= 1
    func_start = index
    some_new_string += 'def'
    some_new_string += some_string[func_start:func_end]
    some_new_string += '(relative):'
    some_new_string += '\n'
    some_new_string += '...'
    return some_new_string

a = '''
on create:
  modifyProp relative width => 11
  modifyProp height => 14
'''
b = pythonicize(a)
print(b)

Outputs:

def create(relative):
...

I'm not really familiar with PLY language, I just got you started so you can finish writing the pythonicize function as you see fit; there may be many edge cases (which I'm unfamiliar with) that you'd have to account for.