def parse_graminit_c(self, filename):
        """Parse the .c file written by pgen.  (Internal)

        The file looks as follows.  The first two lines are always this:

        #include "pgenheaders.h"
        #include "grammar.h"

        After that come four blocks:

        1) one or more state definitions
        2) a table defining dfas
        3) a table defining labels
        4) a struct defining the grammar

        A state definition has the following form:
        - one or more arc arrays, each of the form:
          static arc arcs_<n>_<m>[<k>] = {
                  {<i>, <j>},
                  ...
          };
        - followed by a state array, of the form:
          static state states_<s>[<t>] = {
                  {<k>, arcs_<n>_<m>},
                  ...
          };

        """
        try:
            f = open(filename)
        except OSError as err:
            print(f"Can't open {filename}: {err}")
            return False
        # The code below essentially uses f's iterator-ness!
        lineno = 0

        # Expect the two #include lines
        lineno, line = lineno + 1, next(f)
        assert line == '#include "pgenheaders.h"\n', (lineno, line)
        lineno, line = lineno + 1, next(f)
        assert line == '#include "grammar.h"\n', (lineno, line)

        # Parse the state definitions
        lineno, line = lineno + 1, next(f)
        allarcs = {}
        states = []
        while line.startswith("static arc "):
            while line.startswith("static arc "):
                mo = re.match(r"static arc arcs_(\d+)_(\d+)\[(\d+)\] = {$", line)
                assert mo, (lineno, line)
                n, m, k = list(map(int, mo.groups()))
                arcs = []
                for _ in range(k):
                    lineno, line = lineno + 1, next(f)
                    mo = re.match(r"\s+{(\d+), (\d+)},$", line)
                    assert mo, (lineno, line)
                    i, j = list(map(int, mo.groups()))
                    arcs.append((i, j))
                lineno, line = lineno + 1, next(f)
                assert line == "};\n", (lineno, line)
                allarcs[(n, m)] = arcs
                lineno, line = lineno + 1, next(f)
            mo = re.match(r"static state states_(\d+)\[(\d+)\] = {$", line)
            assert mo, (lineno, line)
            s, t = list(map(int, mo.groups()))
            assert s == len(states), (lineno, line)
            state = []
            for _ in range(t):
                lineno, line = lineno + 1, next(f)
                mo = re.match(r"\s+{(\d+), arcs_(\d+)_(\d+)},$", line)
                assert mo, (lineno, line)
                k, n, m = list(map(int, mo.groups()))
                arcs = allarcs[n, m]
                assert k == len(arcs), (lineno, line)
                state.append(arcs)
            states.append(state)
            lineno, line = lineno + 1, next(f)
            assert line == "};\n", (lineno, line)
            lineno, line = lineno + 1, next(f)
        self.states = states

        # Parse the dfas
        dfas = {}
        mo = re.match(r"static dfa dfas\[(\d+)\] = {$", line)
        assert mo, (lineno, line)
        ndfas = int(mo.group(1))
        for i in range(ndfas):
            lineno, line = lineno + 1, next(f)
            mo = re.match(r'\s+{(\d+), "(\w+)", (\d+), (\d+), states_(\d+),$', line)
            assert mo, (lineno, line)
            symbol = mo.group(2)
            number, x, y, z = list(map(int, mo.group(1, 3, 4, 5)))
            assert self.symbol2number[symbol] == number, (lineno, line)
            assert self.number2symbol[number] == symbol, (lineno, line)
            assert x == 0, (lineno, line)
            state = states[z]
            assert y == len(state), (lineno, line)
            lineno, line = lineno + 1, next(f)
            mo = re.match(r'\s+("(?:\\\d\d\d)*")},$', line)
            assert mo, (lineno, line)
            first = {}
            rawbitset = eval(mo.group(1))
            for i, c in enumerate(rawbitset):
                byte = ord(c)
                for j in range(8):
                    if byte & (1 << j):
                        first[i * 8 + j] = 1
            dfas[number] = (state, first)
        lineno, line = lineno + 1, next(f)
        assert line == "};\n", (lineno, line)
        self.dfas = dfas

        # Parse the labels
        labels = []
        lineno, line = lineno + 1, next(f)
        mo = re.match(r"static label labels\[(\d+)\] = {$", line)
        assert mo, (lineno, line)
        nlabels = int(mo.group(1))
        for i in range(nlabels):
            lineno, line = lineno + 1, next(f)
            mo = re.match(r'\s+{(\d+), (0|"\w+")},$', line)
            assert mo, (lineno, line)
            x, y = mo.groups()
            x = int(x)
            if y == "0":
                y = None
            else:
                y = eval(y)
            labels.append((x, y))
        lineno, line = lineno + 1, next(f)
        assert line == "};\n", (lineno, line)
        self.labels = labels

        # Parse the grammar struct
        lineno, line = lineno + 1, next(f)
        assert line == "grammar _PyParser_Grammar = {\n", (lineno, line)
        lineno, line = lineno + 1, next(f)
        mo = re.match(r"\s+(\d+),$", line)
        assert mo, (lineno, line)
        ndfas = int(mo.group(1))
        assert ndfas == len(self.dfas)
        lineno, line = lineno + 1, next(f)
        assert line == "\tdfas,\n", (lineno, line)
        lineno, line = lineno + 1, next(f)
        mo = re.match(r"\s+{(\d+), labels},$", line)
        assert mo, (lineno, line)
        nlabels = int(mo.group(1))
        assert nlabels == len(self.labels), (lineno, line)
        lineno, line = lineno + 1, next(f)
        mo = re.match(r"\s+(\d+)$", line)
        assert mo, (lineno, line)
        start = int(mo.group(1))
        assert start in self.number2symbol, (lineno, line)
        self.start = start
        lineno, line = lineno + 1, next(f)
        assert line == "};\n", (lineno, line)
        try:
            lineno, line = lineno + 1, next(f)
        except StopIteration:
            pass
        else:
            assert 0, (lineno, line)
Parse the .c file written by pgen.  (Internal)

        The file looks as follows.  The first two lines are always this:

        #include "pgenheaders.h"
        #include "grammar.h"

        After that come four blocks:

        1) one or more state definitions
        2) a table defining dfas
        3) a table defining labels
        4) a struct defining the grammar

        A state definition has the following form:
        - one or more arc arrays, each of the form:
          static arc arcs_<n>_<m>[<k>] = {
                  {<i>, <j>},
                  ...
          };
        - followed by a state array, of the form:
          static state states_<s>[<t>] = {
                  {<k>, arcs_<n>_<m>},
                  ...
          };

        
src/blib2to3/pgen2/conv.py