ENH: str.replace accepts a compiled expression

.str.replace now accepts a compiled regular expression.

See pandas-dev#15446

Author: rouzazari

pandas/core/strings.py

@@ -377,22 +377,29 @@ def str_replace(arr, pat, repl, n=-1, case=True, flags=0):
     # Check whether repl is valid (GH 13438, GH 15055)
     if not (is_string_like(repl) or callable(repl)):
         raise TypeError("repl must be a string or callable")
-    use_re = not case or len(pat) > 1 or flags or callable(repl)
+    is_re = isinstance(pat, re._pattern_type)
+    build_re = not is_re and (not case or len(pat) > 1 or flags or callable(repl))
 
-    if use_re:
+    if is_re:
+        f = _str_replace_regex_func(pat, repl, n)
+    elif build_re:
         if not case:
             flags |= re.IGNORECASE
         regex = re.compile(pat, flags=flags)
-        n = n if n >= 0 else 0
-
-        def f(x):
-            return regex.sub(repl, x, count=n)
+        f = _str_replace_regex_func(regex, repl, n)
     else:
         f = lambda x: x.replace(pat, repl, n)
 
     return _na_map(f, arr)
 
 
+def _str_replace_regex_func(regex, repl, n=-1):
+    n = n if n >= 0 else 0
+    def f(x):
+        return regex.sub(repl, x, count=n)
+    return f
+
+
 def str_repeat(arr, repeats):
     """
     Duplicate each string in the Series/Index by indicated number