logging-not-lazy is emitted when the addition sign is used as well

Close #1479

5 files changed, 41 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 5ffd135d1..1072d4239 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -52,6 +52,9 @@ What's New in Pylint 1.8?
     * Added a new warning, ``raising-format-tuple``, to detect multi-argument
       exception construction instead of message string formatting.
 
+    * Added a new check for method of logging module that concatenate string via + operator
+      Close #1479
+
 What's New in Pylint 1.7.1?
 =========================
 
diff --git a/doc/whatsnew/1.8.rst b/doc/whatsnew/1.8.rst
index f7501ffb2..ba54af9b6 100644
--- a/doc/whatsnew/1.8.rst
+++ b/doc/whatsnew/1.8.rst
@@ -165,6 +165,23 @@ New checkers
 
  .. _PEP479: https://www.python.org/dev/peps/pep-0479
 
+* A new Python checker was added to warn about using a ``+`` operator inside call of logging methods
+  when one of the operands is a litteral string:
+
+  .. code-block:: python
+
+     import logging
+     var = "123"
+     logging.log(logging.INFO, "Var: " + var)
+
+  Instead use formatted string and positional arguments :
+  
+  .. code-block:: python
+
+     import logging
+     var = "123"
+     logging.log(logging.INFO, "Var: %s", var)
+
 Other Changes
 =============
 
diff --git a/pylint/checkers/logging.py b/pylint/checkers/logging.py
index 96edb1d24..f0e7e6440 100644
--- a/pylint/checkers/logging.py
+++ b/pylint/checkers/logging.py
@@ -174,13 +174,24 @@ class LoggingChecker(checkers.BaseChecker):
         else:
             return
 
-        if isinstance(node.args[format_pos], astroid.BinOp) and node.args[format_pos].op == '%':
-            self.add_message('logging-not-lazy', node=node)
+        if isinstance(node.args[format_pos], astroid.BinOp):
+            binop = node.args[format_pos]
+            if (binop.op == '%' or binop.op == '+' and
+                    len([_operand for _operand in (binop.left, binop.right)
+                         if self._is_operand_literal_str(_operand)]) == 1):
+                self.add_message('logging-not-lazy', node=node)
         elif isinstance(node.args[format_pos], astroid.Call):
             self._check_call_func(node.args[format_pos])
         elif isinstance(node.args[format_pos], astroid.Const):
             self._check_format_string(node, format_pos)
 
+    @staticmethod
+    def _is_operand_literal_str(operand):
+        """
+        Return True if the operand in argument is a literal string
+        """
+        return isinstance(operand, astroid.Const) and operand.name == 'str'
+
     def _check_call_func(self, node):
         """Checks that function call is not format_string.format().
 
diff --git a/pylint/test/functional/logging_not_lazy.py b/pylint/test/functional/logging_not_lazy.py
index b843431e4..98eaee08e 100644
--- a/pylint/test/functional/logging_not_lazy.py
+++ b/pylint/test/functional/logging_not_lazy.py
@@ -1,17 +1,22 @@
-# pylint: disable=missing-docstring,no-member,deprecated-method
+# pylint: disable=missing-docstring,no-member,deprecated-method,invalid-name
 
 # Muck up the names in an effort to confuse...
 import logging as renamed_logging
 import os as logging
 
+var = "123"
 # Statements that should be flagged:
 renamed_logging.warn('%s, %s' % (4, 5))             # [logging-not-lazy]
 renamed_logging.exception('%s' % 'Exceptional!')    # [logging-not-lazy]
 renamed_logging.log(renamed_logging.INFO, 'msg: %s' % 'Run!')  # [logging-not-lazy]
+renamed_logging.log(renamed_logging.INFO, "Var: " + var)  # [logging-not-lazy]
 
+var_name = 'Var:'
 # Statements that should not be flagged:
 renamed_logging.warn('%s, %s', 4, 5)
 renamed_logging.log(renamed_logging.INFO, 'msg: %s', 'Run!')
 renamed_logging.warn('%s' + ' the rest of a single string')
+renamed_logging.log(renamed_logging.INFO, var_name + var)
 logging.warn('%s, %s' % (4, 5))
 logging.log(logging.INFO, 'msg: %s' % 'Run!')
+logging.log("Var: " + var)
diff --git a/pylint/test/functional/logging_not_lazy.txt b/pylint/test/functional/logging_not_lazy.txt
index 60c6c5907..5a91369d9 100644
--- a/pylint/test/functional/logging_not_lazy.txt
+++ b/pylint/test/functional/logging_not_lazy.txt
@@ -1,3 +1,4 @@
-logging-not-lazy:8::Specify string format arguments as logging function parameters
 logging-not-lazy:9::Specify string format arguments as logging function parameters
 logging-not-lazy:10::Specify string format arguments as logging function parameters
+logging-not-lazy:11::Specify string format arguments as logging function parameters
+logging-not-lazy:12::Specify string format arguments as logging function parameters