IDLE - remove all bare excepts

[f52c13af-a5a0-4c40-a7a2-6ce855459ec8]

BPO	15313
Nosy	@terryjreedy, @serwy

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields: ```python assignee = 'https://github.com/terryjreedy' closed_at = None created_at = labels = ['expert-IDLE', 'type-bug', '3.7'] title = 'IDLE - remove all bare excepts' updated_at = user = 'https://github.com/serwy' ``` bugs.python.org fields: ```python activity = actor = 'terry.reedy' assignee = 'terry.reedy' closed = False closed_date = None closer = None components = ['IDLE'] creation = creator = 'roger.serwy' dependencies = [] files = [] hgrepos = [] issue_num = 15313 keywords = [] message_count = 5.0 messages = ['165145', '165157', '165162', '165163', '202449'] nosy_count = 2.0 nosy_names = ['terry.reedy', 'roger.serwy'] pr_nums = [] priority = 'normal' resolution = None stage = 'needs patch' status = 'open' superseder = None type = 'behavior' url = 'https://bugs.python.org/issue15313' versions = ['Python 3.6', 'Python 3.7'] ```

[f52c13af-a5a0-4c40-a7a2-6ce855459ec8]

There are a lot of bare exceptions in IDLE. Here's the output of "grep -n 'except:' *.py"

AutoComplete.py:184: except: AutoComplete.py:209: except: Debugger.py:172: except: Debugger.py:344: except: EditorWindow.py:999: except: ObjectBrowser.py:38: except: ObjectBrowser.py:100: except: PyShell.py:133: except: # but debugger may not be active right now.... PyShell.py:154: except: PyShell.py:161: except: PyShell.py:176: except: PyShell.py:433: except: PyShell.py:742: except: PyShell.py:869: except: PyShell.py:1043: except: PyShell.py:1096: except: PyShell.py:1193: except: PyShell.py:1214: except: PyShell.py:1245: except: rpc.py:106: except: rpc.py:206: except: run.py:88: except: run.py:120: except: run.py:125: except: run.py:248: except: run.py:332: except: SearchEngine.py:72: except: StackViewer.py:66: except: WindowList.py:47: except:

Slowly, these exceptions should be refined to include the exact exception being caught.

[terryjreedy]

And possibly change the except clause. The except clause at PyShell 1245 was 'pass', which masked the issue of bpo-13532 and was changed to 'raise' to effectively remove the try: except: to make the unknown problem more visible. It should perhaps be really removed if and when all calls to PyShell.write(s) are properly guarded to make sure 's' is writable.

[f52c13af-a5a0-4c40-a7a2-6ce855459ec8]

Line 1245 is part of this code (in time, these line numbers will change.)

    try:
        self.text.mark_gravity("iomark", "right")
        OutputWindow.write(self, s, tags, "iomark")
        self.text.mark_gravity("iomark", "left")
    except:
        raise ###pass  # ### 11Aug07 KBK if we are expecting exceptions
                       \# let's find out what they are and be specific.

The delegator chain that sits between OutputWindow.write and the Tkinter text.insert method can raise any error. (The ColorDelegator would raise a TypeError when "s" was not a string). I'd rather not replace this with "except Exception:" since the delegators should catch their own errors.

I suggest removing this try/catch block.

[f52c13af-a5a0-4c40-a7a2-6ce855459ec8]

Also, bpo-13582 will become relevant on Windows since modifying the bare excepts may let uncaught exceptions be written to stderr, causing IDLE to crash.

[terryjreedy]

RA's patch for bpo-16261 suggests

diff -r b76d2d8db81f Lib/idlelib/PyShell.py
--- a/Lib/idlelib/PyShell.py    Mon Dec 17 13:43:14 2012 +0530
+++ b/Lib/idlelib/PyShell.py    Wed Jan 09 19:10:26 2013 +0530
@@ -152,7 +152,7 @@
         lineno = int(float(text.index("insert")))
         try:
             self.breakpoints.remove(lineno)
-        except:
+        except ValueError:
             pass
         text.tag_remove("BREAK", "insert linestart",\
                         "insert lineend +1char")