ENH: Allow literal (non-regex) replacement using .str.replace pandas-…

…dev#16808 (pandas-dev#19584)

doc/source/text.rst

@@ -118,8 +118,8 @@ i.e., from the end of the string to the beginning of the string:
 
    s2.str.rsplit('_', expand=True, n=1)
 
-Methods like ``replace`` and ``findall`` take `regular expressions
-<https://docs.python.org/3/library/re.html>`__, too:
+``replace`` by default replaces `regular expressions
+<https://docs.python.org/3/library/re.html>`__:
 
 .. ipython:: python
 
@@ -146,12 +146,25 @@ following code will cause trouble because of the regular expression meaning of
    # We need to escape the special character (for >1 len patterns)
    dollars.str.replace(r'-\$', '-')
 
+.. versionadded:: 0.23.0
+
+If you do want literal replacement of a string (equivalent to
+:meth:`str.replace`), you can set the optional ``regex`` parameter to
+``False``, rather than escaping each character. In this case both ``pat``
+and ``repl`` must be strings:
+
+.. ipython:: python
+
+    # These lines are equivalent
+    dollars.str.replace(r'-\$', '-')
+    dollars.str.replace('-$', '-', regex=False)
+
+.. versionadded:: 0.20.0
+
 The ``replace`` method can also take a callable as replacement. It is called
 on every ``pat`` using :func:`re.sub`. The callable should expect one
 positional argument (a regex object) and return a string.
 
-.. versionadded:: 0.20.0
-
 .. ipython:: python
 
    # Reverse every lowercase alphabetic word
@@ -164,12 +177,12 @@ positional argument (a regex object) and return a string.
    repl = lambda m: m.group('two').swapcase()
    pd.Series(['Foo Bar Baz', np.nan]).str.replace(pat, repl)
 
+.. versionadded:: 0.20.0
+
 The ``replace`` method also accepts a compiled regular expression object
 from :func:`re.compile` as a pattern. All flags should be included in the
 compiled regular expression object.
 
-.. versionadded:: 0.20.0
-
 .. ipython:: python
 
    import re
@@ -186,6 +199,7 @@ regular expression object will raise a ``ValueError``.
     ---------------------------------------------------------------------------
     ValueError: case and flags cannot be set when pat is a compiled regex
 
+
 Indexing with ``.str``
 ----------------------
 
@@ -432,7 +446,7 @@ Method Summary
     :meth:`~Series.str.join`;Join strings in each element of the Series with passed separator
     :meth:`~Series.str.get_dummies`;Split strings on the delimiter returning DataFrame of dummy variables
     :meth:`~Series.str.contains`;Return boolean array if each string contains pattern/regex
-    :meth:`~Series.str.replace`;Replace occurrences of pattern/regex with some other string or the return value of a callable given the occurrence
+    :meth:`~Series.str.replace`;Replace occurrences of pattern/regex/string with some other string or the return value of a callable given the occurrence
     :meth:`~Series.str.repeat`;Duplicate values (``s.str.repeat(3)`` equivalent to ``x * 3``)
     :meth:`~Series.str.pad`;"Add whitespace to left, right, or both sides of strings"
     :meth:`~Series.str.center`;Equivalent to ``str.center``

doc/source/whatsnew/v0.23.0.txt

@@ -620,6 +620,7 @@ Other API Changes
 - Set operations (union, difference...) on :class:`IntervalIndex` with incompatible index types will now raise a ``TypeError`` rather than a ``ValueError`` (:issue:`19329`)
 - :class:`DateOffset` objects render more simply, e.g. ``<DateOffset: days=1>`` instead of ``<DateOffset: kwds={'days': 1}>`` (:issue:`19403`)
 - ``Categorical.fillna`` now validates its ``value`` and ``method`` keyword arguments. It now raises when both or none are specified, matching the behavior of :meth:`Series.fillna` (:issue:`19682`)
+- :func:`Series.str.replace` now takes an optional `regex` keyword which, when set to ``False``, uses literal string replacement rather than regex replacement (:issue:`16808`)
 
 .. _whatsnew_0230.deprecations:
 

pandas/core/strings.py

@@ -306,7 +306,7 @@ def str_endswith(arr, pat, na=np.nan):
     return _na_map(f, arr, na, dtype=bool)
 
 
-def str_replace(arr, pat, repl, n=-1, case=None, flags=0):
+def str_replace(arr, pat, repl, n=-1, case=None, flags=0, regex=True):
     r"""
     Replace occurrences of pattern/regex in the Series/Index with
     some other string. Equivalent to :meth:`str.replace` or
@@ -337,25 +337,50 @@ def str_replace(arr, pat, repl, n=-1, case=None, flags=0):
     flags : int, default 0 (no flags)
         - re module flags, e.g. re.IGNORECASE
         - Cannot be set if `pat` is a compiled regex
+    regex : boolean, default True
+        - If True, assumes the passed-in pattern is a regular expression.
+        - If False, treats the pattern as a literal string
+        - Cannot be set to False if `pat` is a compiled regex or `repl` is
+          a callable.
+
+        .. versionadded:: 0.23.0
 
     Returns
     -------
     replaced : Series/Index of objects
 
+    Raises
+    ------
+    ValueError
+        * if `regex` is False and `repl` is a callable or `pat` is a compiled
+          regex
+        * if `pat` is a compiled regex and `case` or `flags` is set
+
     Notes
     -----
     When `pat` is a compiled regex, all flags should be included in the
-    compiled regex. Use of `case` or `flags` with a compiled regex will
-    raise an error.
+    compiled regex. Use of `case`, `flags`, or `regex=False` with a compiled
+    regex will raise an error.
 
     Examples
     --------
-    When `repl` is a string, every `pat` is replaced as with
-    :meth:`str.replace`. NaN value(s) in the Series are left as is.
+    When `pat` is a string and `regex` is True (the default), the given `pat`
+    is compiled as a regex. When `repl` is a string, it replaces matching
+    regex patterns as with :meth:`re.sub`. NaN value(s) in the Series are
+    left as is:
+
+    >>> pd.Series(['foo', 'fuz', np.nan]).str.replace('f.', 'ba', regex=True)
+    0    bao
+    1    baz
+    2    NaN
+    dtype: object
 
-    >>> pd.Series(['foo', 'fuz', np.nan]).str.replace('f', 'b')
-    0    boo
-    1    buz
+    When `pat` is a string and `regex` is False, every `pat` is replaced with
+    `repl` as with :meth:`str.replace`:
+
+    >>> pd.Series(['f.o', 'fuz', np.nan]).str.replace('f.', 'ba', regex=False)
+    0    bao
+    1    fuz
     2    NaN
     dtype: object
 
@@ -397,34 +422,41 @@ def str_replace(arr, pat, repl, n=-1, case=None, flags=0):
     1    bar
     2    NaN
     dtype: object
+
     """
 
     # 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")
 
     is_compiled_re = is_re(pat)
-    if is_compiled_re:
-        if (case is not None) or (flags != 0):
-            raise ValueError("case and flags cannot be set"
-                             " when pat is a compiled regex")
-    else:
-        # not a compiled regex
-        # set default case
-        if case is None:
-            case = True
-
-        # add case flag, if provided
-        if case is False:
-            flags |= re.IGNORECASE
-
-    use_re = is_compiled_re or len(pat) > 1 or flags or callable(repl)
-
-    if use_re:
-        n = n if n >= 0 else 0
-        regex = re.compile(pat, flags=flags)
-        f = lambda x: regex.sub(repl=repl, string=x, count=n)
+    if regex:
+        if is_compiled_re:
+            if (case is not None) or (flags != 0):
+                raise ValueError("case and flags cannot be set"
+                                 " when pat is a compiled regex")
+        else:
+            # not a compiled regex
+            # set default case
+            if case is None:
+                case = True
+
+            # add case flag, if provided
+            if case is False:
+                flags |= re.IGNORECASE
+        if is_compiled_re or len(pat) > 1 or flags or callable(repl):
+            n = n if n >= 0 else 0
+            compiled = re.compile(pat, flags=flags)
+            f = lambda x: compiled.sub(repl=repl, string=x, count=n)
+        else:
+            f = lambda x: x.replace(pat, repl, n)
     else:
+        if is_compiled_re:
+            raise ValueError("Cannot use a compiled regex as replacement "
+                             "pattern with regex=False")
+        if callable(repl):
+            raise ValueError("Cannot use a callable replacement when "
+                             "regex=False")
         f = lambda x: x.replace(pat, repl, n)
 
     return _na_map(f, arr)
@@ -1596,9 +1628,9 @@ def match(self, pat, case=True, flags=0, na=np.nan, as_indexer=None):
         return self._wrap_result(result)
 
     @copy(str_replace)
-    def replace(self, pat, repl, n=-1, case=None, flags=0):
+    def replace(self, pat, repl, n=-1, case=None, flags=0, regex=True):
         result = str_replace(self._data, pat, repl, n=n, case=case,
-                             flags=flags)
+                             flags=flags, regex=regex)
         return self._wrap_result(result)
 
     @copy(str_repeat)

pandas/tests/test_strings.py

@@ -530,6 +530,27 @@ def test_replace_compiled_regex(self):
         exp = Series(['foObaD__baRbaD', NA])
         tm.assert_series_equal(result, exp)
 
+    def test_replace_literal(self):
+        # GH16808 literal replace (regex=False vs regex=True)
+        values = Series(['f.o', 'foo', NA])
+        exp = Series(['bao', 'bao', NA])
+        result = values.str.replace('f.', 'ba')
+        tm.assert_series_equal(result, exp)
+
+        exp = Series(['bao', 'foo', NA])
+        result = values.str.replace('f.', 'ba', regex=False)
+        tm.assert_series_equal(result, exp)
+
+        # Cannot do a literal replace if given a callable repl or compiled
+        # pattern
+        callable_repl = lambda m: m.group(0).swapcase()
+        compiled_pat = re.compile('[a-z][A-Z]{2}')
+
+        pytest.raises(ValueError, values.str.replace, 'abc', callable_repl,
+                      regex=False)
+        pytest.raises(ValueError, values.str.replace, compiled_pat, '',
+                      regex=False)
+
     def test_repeat(self):
         values = Series(['a', 'b', NA, 'c', NA, 'd'])