factored out regex generation

Former-commit-id: 476a909e4d

scripts/gen_regex.py

@@ -0,0 +1,39 @@
+import argparse
+import unicodedata
+
+def func_to_regex(accept):
+    """
+    Converts a function that accepts a single unicode character into a regex.
+    Unassigned unicode characters are treated like their neighbors.
+    """
+    ranges = []
+    start = None
+    has_accepted = False
+    for x in range(0x110000):
+        c = chr(x)
+
+        if accept(c):
+            has_accepted = True
+            if start is None:
+                start = None
+        elif unicodedata.category(c) == 'Cn':
+            if start is None:
+                start = c
+        elif start is not None:
+            if has_accepted:
+                ranges.append('-'.join([start, chr(x-1)]))
+                has_accepted = False
+            start = None
+    else:
+        if has_accepted and start is not None:
+            ranges.append('-'.join([start, chr(x-1)]))
+
+    return '[%s]' % ''.join(ranges)
+
+if __name__ == '__main__':
+    import argparse
+
+    parser = argparse.ArgumentParser(description='Generate a regex matching a function')
+    parser.add_argument('acceptor', help='an python function that accepts a single char')
+    args = parser.parse_args()
+    print(func_to_regex(eval(args.acceptor)))