1 files changed, 51 insertions, 0 deletions
diff --git a/pycodestyle.py b/pycodestyle.py
index 5b7a39c..d31ac9e 100755
--- a/pycodestyle.py
+++ b/pycodestyle.py
@@ -1388,6 +1388,57 @@ def python_3000_backticks(logical_line):
         yield pos, "W604 backticks are deprecated, use 'repr()'"
 
 
+@register_check
+def python_3000_invalid_escape_sequence(logical_line, tokens):
+    r"""Invalid escape sequences are deprecated in Python 3.6.
+
+    Okay: regex = r'\.png$'
+    W605: regex = '\.png$'
+    """
+    # https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals
+    valid = [
+        '\n',
+        '\\',
+        '\'',
+        '"',
+        'a',
+        'b',
+        'f',
+        'n',
+        'r',
+        't',
+        'v',
+        '0', '1', '2', '3', '4', '5', '6', '7',
+        'x',
+
+        # Escape sequences only recognized in string literals
+        'N',
+        'u',
+        'U',
+    ]
+
+    for token_type, text, start, end, line in tokens:
+        if token_type == tokenize.STRING:
+            quote = text[-3:] if text[-3:] in ('"""', "'''") else text[-1]
+            # Extract string modifiers (e.g. u or r)
+            quote_pos = text.index(quote)
+            prefix = text[:quote_pos].lower()
+            start = quote_pos + len(quote)
+            string = text[start:-len(quote)]
+
+            if 'r' not in prefix:
+                pos = string.find('\\')
+                while pos >= 0:
+                    pos += 1
+                    if string[pos] not in valid:
+                        yield (
+                            pos,
+                            "W605 invalid escape sequence '\\%s'" %
+                            string[pos],
+                        )
+                    pos = string.find('\\', pos + 1)
+
+
 ##############################################################################
 # Helper functions
 ##############################################################################