warn about bare except clause

Author: rogalski

CHANGES.txt

@@ -28,6 +28,7 @@ Changes:
 * Report E741 on 'global' and 'nonlocal' statements, as well as prohibited
   single-letter variables.
 * Deprecated use of `[pep8]` section name in favor of `[pycodestyle]`; #591
+* Report E722 when bare except clause is used; #579
 
 Bugs:
 

docs/intro.rst

@@ -361,6 +361,8 @@ This is the current list of error and warning codes:
 +------------+----------------------------------------------------------------------+
 | E721 (^)   | do not compare types, use 'isinstance()'                             |
 +------------+----------------------------------------------------------------------+
+| E722       | do not use bare except, specify exception instead                    |
++------------+----------------------------------------------------------------------+
 | E731       | do not assign a lambda expression, use a def                         |
 +------------+----------------------------------------------------------------------+
 | E741       | do not use variables named 'l', 'O', or 'I'                          |

pycodestyle.py

@@ -912,8 +912,10 @@ def module_imports_on_top_of_file(
     Okay: # this is a comment\nimport os
     Okay: '''this is a module docstring'''\nimport os
     Okay: r'''this is a module docstring'''\nimport os
-    Okay: try:\n    import x\nexcept:\n    pass\nelse:\n    pass\nimport y
-    Okay: try:\n    import x\nexcept:\n    pass\nfinally:\n    pass\nimport y
+    Okay:
+    try:\n\timport x\nexcept ImportError:\n\tpass\nelse:\n\tpass\nimport y
+    Okay:
+    try:\n\timport x\nexcept ImportError:\n\tpass\nfinally:\n\tpass\nimport y
     E402: a=1\nimport os
     E402: 'One string'\n"Two string"\nimport os
     E402: a=1\nfrom sys import x
@@ -1179,6 +1181,22 @@ def comparison_type(logical_line, noqa):
         yield match.start(), "E721 do not compare types, use 'isinstance()'"
 
 
+def bare_except(logical_line, noqa):
+    r"""When catching exceptions, mention specific exceptions whenever possible.
+
+    Okay: except Exception:
+    Okay: except BaseException:
+    E722: except:
+    """
+    if noqa:
+        return
+
+    regex = re.compile(r"except\s*:")
+    match = regex.match(logical_line)
+    if match:
+        yield match.start(), "E722 do not use bare except'"
+
+
 def ambiguous_identifier(logical_line, tokens):
     r"""Never use the characters 'l', 'O', or 'I' as variable names.
 

testsuite/E30.py

@@ -113,7 +113,7 @@ def a():
 
 try:
     a()
-except:
+except Exception:
     pass
 #: E305:5:1
 def a():

testsuite/E40.py

@@ -18,7 +18,7 @@
 #: Okay
 try:
     import foo
-except:
+except ImportError:
     pass
 else:
     print('imported foo')

testsuite/E72.py

@@ -49,3 +49,31 @@
     pass
 if type(a) != type(b) or type(a) == type(ccc):
     pass
+#: E722
+try:
+    pass
+except:
+    pass
+#: E722
+try:
+    pass
+except Exception:
+    pass
+except:
+    pass
+#: E722 E203 E271
+try:
+    pass
+except  :
+    pass
+#: Okay
+fake_code = """"
+try:
+    do_something()
+except:
+    pass
+"""
+try:
+    pass
+except Exception:
+    pass