//  [c]
tok_get(struct tok_state *tok, char **p_start, char **p_end)
{
    int c;
    int blankline, nonascii;

    *p_start = *p_end = NULL;
  nextline:
    tok->start = NULL;
    blankline = 0;

    /* Get indentation level */
    if (tok->atbol) {
        int col = 0;
        int altcol = 0;
        tok->atbol = 0;
        for (;;) {
            c = tok_nextc(tok);
            if (c == ' ') {
                col++, altcol++;
            }
            else if (c == '\t') {
                col = (col / tok->tabsize + 1) * tok->tabsize;
                altcol = (altcol / ALTTABSIZE + 1) * ALTTABSIZE;
            }
            else if (c == '\014')  {/* Control-L (formfeed) */
                col = altcol = 0; /* For Emacs users */
            }
            else {
                break;
            }
        }
        tok_backup(tok, c);
        if (c == '#' || c == '\n') {
            /* Lines with only whitespace and/or comments
               shouldn't affect the indentation and are
               not passed to the parser as NEWLINE tokens,
               except *totally* empty lines in interactive
               mode, which signal the end of a command group. */
            if (col == 0 && c == '\n' && tok->prompt != NULL) {
                blankline = 0; /* Let it through */
            }
            else {
                blankline = 1; /* Ignore completely */
            }
            /* We can't jump back right here since we still
               may need to skip to the end of a comment */
        }
        if (!blankline && tok->level == 0) {
            if (col == tok->indstack[tok->indent]) {
                /* No change */
                if (altcol != tok->altindstack[tok->indent]) {
                    return indenterror(tok);
                }
            }
            else if (col > tok->indstack[tok->indent]) {
                /* Indent -- always one */
                if (tok->indent+1 >= MAXINDENT) {
                    tok->done = E_TOODEEP;
                    tok->cur = tok->inp;
                    return ERRORTOKEN;
                }
                if (altcol <= tok->altindstack[tok->indent]) {
                    return indenterror(tok);
                }
                tok->pendin++;
                tok->indstack[++tok->indent] = col;
                tok->altindstack[tok->indent] = altcol;
            }
            else /* col < tok->indstack[tok->indent] */ {
                /* Dedent -- any number, must be consistent */
                while (tok->indent > 0 &&
                    col < tok->indstack[tok->indent]) {
                    tok->pendin--;
                    tok->indent--;
                }
                if (col != tok->indstack[tok->indent]) {
                    tok->done = E_DEDENT;
                    tok->cur = tok->inp;
                    return ERRORTOKEN;
                }
                if (altcol != tok->altindstack[tok->indent]) {
                    return indenterror(tok);
                }
            }
        }
    }

    tok->start = tok->cur;

    /* Return pending indents/dedents */
    if (tok->pendin != 0) {
        if (tok->pendin < 0) {
            tok->pendin++;
            return DEDENT;
        }
        else {
            tok->pendin--;
            return INDENT;
        }
    }

 again:
    tok->start = NULL;
    /* Skip spaces */
    do {
        c = tok_nextc(tok);
    } while (c == ' ' || c == '\t' || c == '\014');

    /* Set start of current token */
    tok->start = tok->cur - 1;

    /* Skip comment */
    if (c == '#') {
        while (c != EOF && c != '\n') {
            c = tok_nextc(tok);
        }
    }

    /* Check for EOF and errors now */
    if (c == EOF) {
        return tok->done == E_EOF ? ENDMARKER : ERRORTOKEN;
    }

    /* Identifier (most frequent token!) */
    nonascii = 0;
    if (is_potential_identifier_start(c)) {
        /* Process the various legal combinations of b"", r"", u"", and f"". */
        int saw_b = 0, saw_r = 0, saw_u = 0, saw_f = 0;
        while (1) {
            if (!(saw_b || saw_u || saw_f) && (c == 'b' || c == 'B'))
                saw_b = 1;
            /* Since this is a backwards compatibility support literal we don't
               want to support it in arbitrary order like byte literals. */
            else if (!(saw_b || saw_u || saw_r || saw_f)
                     && (c == 'u'|| c == 'U')) {
                saw_u = 1;
            }
            /* ur"" and ru"" are not supported */
            else if (!(saw_r || saw_u) && (c == 'r' || c == 'R')) {
                saw_r = 1;
            }
            else if (!(saw_f || saw_b || saw_u) && (c == 'f' || c == 'F')) {
                saw_f = 1;
            }
            else {
                break;
            }
            c = tok_nextc(tok);
            if (c == '"' || c == '\'') {
                goto letter_quote;
            }
        }
        while (is_potential_identifier_char(c)) {
            if (c >= 128) {
                nonascii = 1;
            }
            c = tok_nextc(tok);
        }
        tok_backup(tok, c);
        if (nonascii && !verify_identifier(tok)) {
            return ERRORTOKEN;
        }
        *p_start = tok->start;
        *p_end = tok->cur;

        return NAME;
    }

    /* Newline */
    if (c == '\n') {
        tok->atbol = 1;
        if (blankline || tok->level > 0) {
            goto nextline;
        }
        *p_start = tok->start;
        *p_end = tok->cur - 1; /* Leave '\n' out of the string */
        tok->cont_line = 0;
        return NEWLINE;
    }

    /* Period or number starting with period? */
    if (c == '.') {
        c = tok_nextc(tok);
        if (isdigit(c)) {
            goto fraction;
        } else if (c == '.') {
            c = tok_nextc(tok);
            if (c == '.') {
                *p_start = tok->start;
                *p_end = tok->cur;
                return ELLIPSIS;
            }
            else {
                tok_backup(tok, c);
            }
            tok_backup(tok, '.');
        }
        else {
            tok_backup(tok, c);
        }
        *p_start = tok->start;
        *p_end = tok->cur;
        return DOT;
    }

    /* Number */
    if (isdigit(c)) {
        if (c == '0') {
            /* Hex, octal or binary -- maybe. */
            c = tok_nextc(tok);
            if (c == 'x' || c == 'X') {
                /* Hex */
                c = tok_nextc(tok);
                do {
                    if (c == '_') {
                        c = tok_nextc(tok);
                    }
                    if (!isxdigit(c)) {
                        tok_backup(tok, c);
                        return syntaxerror(tok, "invalid hexadecimal literal");
                    }
                    do {
                        c = tok_nextc(tok);
                    } while (isxdigit(c));
                } while (c == '_');
            }
            else if (c == 'o' || c == 'O') {
                /* Octal */
                c = tok_nextc(tok);
                do {
                    if (c == '_') {
                        c = tok_nextc(tok);
                    }
                    if (c < '0' || c >= '8') {
                        tok_backup(tok, c);
                        if (isdigit(c)) {
                            return syntaxerror(tok,
                                    "invalid digit '%c' in octal literal", c);
                        }
                        else {
                            return syntaxerror(tok, "invalid octal literal");
                        }
                    }
                    do {
                        c = tok_nextc(tok);
                    } while ('0' <= c && c < '8');
                } while (c == '_');
                if (isdigit(c)) {
                    return syntaxerror(tok,
                            "invalid digit '%c' in octal literal", c);
                }
            }
            else if (c == 'b' || c == 'B') {
                /* Binary */
                c = tok_nextc(tok);
                do {
                    if (c == '_') {
                        c = tok_nextc(tok);
                    }
                    if (c != '0' && c != '1') {
                        tok_backup(tok, c);
                        if (isdigit(c)) {
                            return syntaxerror(tok,
                                    "invalid digit '%c' in binary literal", c);
                        }
                        else {
                            return syntaxerror(tok, "invalid binary literal");
                        }
                    }
                    do {
                        c = tok_nextc(tok);
                    } while (c == '0' || c == '1');
                } while (c == '_');
                if (isdigit(c)) {
                    return syntaxerror(tok,
                            "invalid digit '%c' in binary literal", c);
                }
            }
            else {
                int nonzero = 0;
                /* maybe old-style octal; c is first char of it */
                /* in any case, allow '0' as a literal */
                while (1) {
                    if (c == '_') {
                        c = tok_nextc(tok);
                        if (!isdigit(c)) {
                            tok_backup(tok, c);
                            return syntaxerror(tok, "invalid decimal literal");
                        }
                    }
                    if (c != '0') {
                        break;
                    }
                    c = tok_nextc(tok);
                }
                if (isdigit(c)) {
                    nonzero = 1;
                    c = tok_decimal_tail(tok);
                    if (c == 0) {
                        return ERRORTOKEN;
                    }
                }
                if (c == '.') {
                    c = tok_nextc(tok);
                    goto fraction;
                }
                else if (c == 'e' || c == 'E') {
                    goto exponent;
                }
                else if (c == 'j' || c == 'J') {
                    goto imaginary;
                }
                else if (nonzero) {
                    /* Old-style octal: now disallowed. */
                    tok_backup(tok, c);
                    return syntaxerror(tok,
                                       "leading zeros in decimal integer "
                                       "literals are not permitted; "
                                       "use an 0o prefix for octal integers");
                }
            }
        }
        else {
            /* Decimal */
            c = tok_decimal_tail(tok);
            if (c == 0) {
                return ERRORTOKEN;
            }
            {
                /* Accept floating point numbers. */
                if (c == '.') {
                    c = tok_nextc(tok);
        fraction:
                    /* Fraction */
                    if (isdigit(c)) {
                        c = tok_decimal_tail(tok);
                        if (c == 0) {
                            return ERRORTOKEN;
                        }
                    }
                }
                if (c == 'e' || c == 'E') {
                    int e;
                  exponent:
                    e = c;
                    /* Exponent part */
                    c = tok_nextc(tok);
                    if (c == '+' || c == '-') {
                        c = tok_nextc(tok);
                        if (!isdigit(c)) {
                            tok_backup(tok, c);
                            return syntaxerror(tok, "invalid decimal literal");
                        }
                    } else if (!isdigit(c)) {
                        tok_backup(tok, c);
                        tok_backup(tok, e);
                        *p_start = tok->start;
                        *p_end = tok->cur;
                        return NUMBER;
                    }
                    c = tok_decimal_tail(tok);
                    if (c == 0) {
                        return ERRORTOKEN;
                    }
                }
                if (c == 'j' || c == 'J') {
                    /* Imaginary part */
        imaginary:
                    c = tok_nextc(tok);
                }
            }
        }
        tok_backup(tok, c);
        *p_start = tok->start;
        *p_end = tok->cur;
        return NUMBER;
    }

  letter_quote:
    /* String */
    if (c == '\'' || c == '"') {
        int quote = c;
        int quote_size = 1;             /* 1 or 3 */
        int end_quote_size = 0;

        /* Nodes of type STRING, especially multi line strings
           must be handled differently in order to get both
           the starting line number and the column offset right.
           (cf. issue 16806) */
        tok->first_lineno = tok->lineno;
        tok->multi_line_start = tok->line_start;

        /* Find the quote size and start of string */
        c = tok_nextc(tok);
        if (c == quote) {
            c = tok_nextc(tok);
            if (c == quote) {
                quote_size = 3;
            }
            else {
                end_quote_size = 1;     /* empty string found */
            }
        }
        if (c != quote) {
            tok_backup(tok, c);
        }

        /* Get rest of string */
        while (end_quote_size != quote_size) {
            c = tok_nextc(tok);
            if (c == EOF) {
                if (quote_size == 3) {
                    tok->done = E_EOFS;
                }
                else {
                    tok->done = E_EOLS;
                }
                tok->cur = tok->inp;
                return ERRORTOKEN;
            }
            if (quote_size == 1 && c == '\n') {
                tok->done = E_EOLS;
                tok->cur = tok->inp;
                return ERRORTOKEN;
            }
            if (c == quote) {
                end_quote_size += 1;
            }
            else {
                end_quote_size = 0;
                if (c == '\\') {
                    tok_nextc(tok);  /* skip escaped char */
                }
            }
        }

        *p_start = tok->start;
        *p_end = tok->cur;
        return STRING;
    }

    /* Line continuation */
    if (c == '\\') {
        c = tok_nextc(tok);
        if (c != '\n') {
            tok->done = E_LINECONT;
            tok->cur = tok->inp;
            return ERRORTOKEN;
        }
        tok->cont_line = 1;
        goto again; /* Read next line */
    }

    /* Check for two-character token */
    {
        int c2 = tok_nextc(tok);
        int token = PyToken_TwoChars(c, c2);
        if (token != OP) {
            int c3 = tok_nextc(tok);
            int token3 = PyToken_ThreeChars(c, c2, c3);
            if (token3 != OP) {
                token = token3;
            }
            else {
                tok_backup(tok, c3);
            }
            *p_start = tok->start;
            *p_end = tok->cur;
            return token;
        }
        tok_backup(tok, c2);
    }

    /* Keep track of parentheses nesting level */
    switch (c) {
    case '(':
    case '[':
    case '{':
#ifndef PGEN
        if (tok->level >= MAXLEVEL) {
            return syntaxerror(tok, "too many nested parentheses");
        }
        tok->parenstack[tok->level] = c;
        tok->parenlinenostack[tok->level] = tok->lineno;
#endif
        tok->level++;
        break;
    case ')':
    case ']':
    case '}':
#ifndef PGEN
        if (!tok->level) {
            return syntaxerror(tok, "unmatched '%c'", c);
        }
#endif
        tok->level--;
#ifndef PGEN
        int opening = tok->parenstack[tok->level];
        if (!((opening == '(' && c == ')') ||
              (opening == '[' && c == ']') ||
              (opening == '{' && c == '}')))
        {
            if (tok->parenlinenostack[tok->level] != tok->lineno) {
                return syntaxerror(tok,
                        "closing parenthesis '%c' does not match "
                        "opening parenthesis '%c' on line %d",
                        c, opening, tok->parenlinenostack[tok->level]);
            }
            else {
                return syntaxerror(tok,
                        "closing parenthesis '%c' does not match "
                        "opening parenthesis '%c'",
                        c, opening);
            }
        }
#endif
        break;
    }

    /* Punctuation character */
    *p_start = tok->start;
    *p_end = tok->cur;
    return PyToken_OneChar(c);
}