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ENH: str.replace accepts a compiled expression
.str.replace now accepts a compiled regular expression for `pat`. See #15446
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-9
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3 files changed

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doc/source/whatsnew/v0.20.0.txt

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@@ -28,6 +28,7 @@ New features
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- Integration with the ``feather-format``, including a new top-level ``pd.read_feather()`` and ``DataFrame.to_feather()`` method, see :ref:`here <io.feather>`.
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- ``.str.replace`` now accepts a callable, as replacement, which is passed to ``re.sub`` (:issue:`15055`)
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- ``.str.replace`` now accepts a compiled regular expression as pattern (:issue:`15446`)
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pandas/core/strings.py

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@@ -21,6 +21,7 @@
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import warnings
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import textwrap
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import codecs
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from functools import partial
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_cpython_optimized_encoders = (
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"utf-8", "utf8", "latin-1", "latin1", "iso-8859-1", "mbcs", "ascii"
@@ -311,8 +312,12 @@ def str_replace(arr, pat, repl, n=-1, case=True, flags=0):
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Parameters
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----------
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pat : string
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Character sequence or regular expression
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pat : string or compiled regex
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String can be a character sequence or regular expression.
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.. versionadded:: 0.20.0
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`pat` also accepts a compiled regex.
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repl : string or callable
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Replacement string or a callable. The callable is passed the regex
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match object and must return a replacement string to be used.
@@ -324,9 +329,10 @@ def str_replace(arr, pat, repl, n=-1, case=True, flags=0):
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n : int, default -1 (all)
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Number of replacements to make from start
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case : boolean, default True
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If True, case sensitive
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If True, case sensitive. Ignored if `pat` is a compiled regex.
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flags : int, default 0 (no flags)
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re module flags, e.g. re.IGNORECASE
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re module flags, e.g. re.IGNORECASE. Ignored if `pat` is a compiled
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regex.
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Returns
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-------
@@ -372,21 +378,33 @@ def str_replace(arr, pat, repl, n=-1, case=True, flags=0):
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0 tWO
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1 bAR
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dtype: object
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When `pat` is a compiled regex, all flags should be included in the
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compiled regex. Use of `case` and `flags` with a compiled regex will
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raise an error.
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>>> regex_pat = re.compile(r'FUZ', flags=re.IGNORECASE)
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>>> pd.Series(['foo', 'fuz', np.nan]).str.replace(regex_pat, 'bar')
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0 foo
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1 bar
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2 NaN
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dtype: object
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"""
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# Check whether repl is valid (GH 13438, GH 15055)
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if not (is_string_like(repl) or callable(repl)):
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raise TypeError("repl must be a string or callable")
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use_re = not case or len(pat) > 1 or flags or callable(repl)
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# Check whether pat is a compiled regex or should be compiled
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is_compiled_re = isinstance(pat, type(re.compile("")))
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use_re = (is_compiled_re or not case or
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len(pat) > 1 or flags or callable(repl))
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if use_re:
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if not case:
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flags |= re.IGNORECASE
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regex = re.compile(pat, flags=flags)
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n = n if n >= 0 else 0
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def f(x):
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return regex.sub(repl, x, count=n)
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f = lambda x: partial(re.sub, pattern=pat, repl=repl,
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count=n, flags=flags)(string=x)
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else:
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f = lambda x: x.replace(pat, repl, n)
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pandas/tests/test_strings.py

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@@ -469,6 +469,62 @@ def test_replace_callable(self):
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exp = Series(['bAR', NA])
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tm.assert_series_equal(result, exp)
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def test_replace_compiled_regex(self):
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# GH 15446
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values = Series(['fooBAD__barBAD', NA])
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# test with compiled regex
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pat = re.compile(r'BAD[_]*')
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result = values.str.replace(pat, '')
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exp = Series(['foobar', NA])
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tm.assert_series_equal(result, exp)
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# mixed
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mixed = Series(['aBAD', NA, 'bBAD', True, datetime.today(), 'fooBAD',
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None, 1, 2.])
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rs = Series(mixed).str.replace(pat, '')
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xp = Series(['a', NA, 'b', NA, NA, 'foo', NA, NA, NA])
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tm.assertIsInstance(rs, Series)
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tm.assert_almost_equal(rs, xp)
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# unicode
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values = Series([u('fooBAD__barBAD'), NA])
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result = values.str.replace(pat, '')
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exp = Series([u('foobar'), NA])
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tm.assert_series_equal(result, exp)
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result = values.str.replace(pat, '', n=1)
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exp = Series([u('foobarBAD'), NA])
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tm.assert_series_equal(result, exp)
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# flags + unicode
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values = Series([b"abcd,\xc3\xa0".decode("utf-8")])
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exp = Series([b"abcd, \xc3\xa0".decode("utf-8")])
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pat = re.compile(r"(?<=\w),(?=\w)", flags=re.UNICODE)
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result = values.str.replace(pat, ", ")
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tm.assert_series_equal(result, exp)
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# case and flags provided to str.replace will have no effect
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# and will produce warnings
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values = Series(['fooBAD__barBAD__bad', NA])
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pat = re.compile(r'BAD[_]*')
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with tm.assertRaisesRegexp(ValueError, "process flags argument"):
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result = values.str.replace(pat, '', flags=re.IGNORECASE)
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with tm.assertRaisesRegexp(ValueError, "process flags argument"):
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result = values.str.replace(pat, '', case=False)
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# test with callable
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values = Series(['fooBAD__barBAD', NA])
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repl = lambda m: m.group(0).swapcase()
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pat = re.compile('[a-z][A-Z]{2}')
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result = values.str.replace(pat, repl, n=2)
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exp = Series(['foObaD__baRbaD', NA])
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tm.assert_series_equal(result, exp)
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def test_repeat(self):
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values = Series(['a', 'b', NA, 'c', NA, 'd'])
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