.. _anomalous-backslash-in-string:

anomalous-backslash-in-string / W1401
=====================================

**Message emitted:**

``Anomalous backslash in string: '%s'. String constant might be missing an r prefix.``

**Description:**

*Used when a backslash is in a literal string but not as an escape.*

**Problematic code:**

.. literalinclude:: /data/messages/a/anomalous-backslash-in-string/bad.py
   :language: python

**Correct code:**

``double_escape.py``:

.. literalinclude:: /data/messages/a/anomalous-backslash-in-string/good/double_escape.py
    :language: python


``existing_escape_sequence.py``:

.. literalinclude:: /data/messages/a/anomalous-backslash-in-string/good/existing_escape_sequence.py
    :language: python


``r_prefix.py``:

.. literalinclude:: /data/messages/a/anomalous-backslash-in-string/good/r_prefix.py
    :language: python



**Additional details:**

``\z`` is same as ``\\z`` because there's no escape sequence for ``z``. But it is not clear
for the reader of the code.

**Related links:**

- `String and Bytes literals <https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals>`_
- `Long form stackoverflow explanation  <https://stackoverflow.com/a/19030982/2519059>`_


Created by the `string <https://github.com/pylint-dev/pylint/blob/main/pylint/checkers/strings.py>`__ checker.