fix bug about fetching knowledge graph (#3394)

### What problem does this PR solve?


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

deepdoc/parser/txt_parser.py

@@ -10,6 +10,8 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 #
+import re
+
 from deepdoc.parser.utils import get_text
 from rag.nlp import num_tokens_from_string
 
@@ -29,8 +31,6 @@ class RAGFlowTxtParser:
         def add_chunk(t):
             nonlocal cks, tk_nums, delimiter
             tnum = num_tokens_from_string(t)
-            if tnum < 8:
-                pos = ""
             if tk_nums[-1] > chunk_token_num:
                 cks.append(t)
                 tk_nums.append(tnum)
@@ -38,15 +38,19 @@ class RAGFlowTxtParser:
                 cks[-1] += t
                 tk_nums[-1] += tnum
 
-        s, e = 0, 1
-        while e < len(txt):
-            if txt[e] in delimiter:
-                add_chunk(txt[s: e + 1])
-                s = e + 1
-                e = s + 1
-            else:
-                e += 1
-        if s < e:
-            add_chunk(txt[s: e + 1])
+        dels = []
+        s = 0
+        for m in re.finditer(r"`([^`]+)`", delimiter, re.I):
+            f, t = m.span()
+            dels.append(m.group(1))
+            dels.extend(list(delimiter[s: f]))
+            s = t
+        if s < len(delimiter):
+            dels.extend(list(delimiter[s:]))
+        dels = [re.escape(d) for d in delimiter if d]
+        dels = [d for d in dels if d]
+        dels = "|".join(dels)
+        secs = re.split(r"(%s)" % dels, txt)
+        for sec in secs: add_chunk(sec)
 
-        return [[c,""] for c in cks]
+        return [[c, ""] for c in cks]