python -c: Line causing exception not shown for exceptions other than SyntaxErrors

[Arfrever]

BPO	23035
Nosy	@terryjreedy, @pitrou, @vstinner, @benjaminp, @serhiy-storchaka

^{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:

assignee = None
closed_at = None
created_at = <Date 2014-12-12.01:44:07.380>
labels = ['interpreter-core', 'type-feature', '3.11']
title = 'python -c: Line causing exception not shown for exceptions other than SyntaxErrors'
updated_at = <Date 2021-06-15.16:58:00.697>
user = 'https://bugs.python.org/Arfrever'

bugs.python.org fields:

activity = <Date 2021-06-15.16:58:00.697>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2014-12-12.01:44:07.380>
creator = 'Arfrever'
dependencies = []
files = []
hgrepos = []
issue_num = 23035
keywords = []
message_count = 7.0
messages = ['232506', '232537', '232578', '232582', '232583', '232584', '232585']
nosy_count = 6.0
nosy_names = ['terry.reedy', 'pitrou', 'vstinner', 'benjamin.peterson', 'Arfrever', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue23035'
versions = ['Python 3.11']

Linked PRs

• gh-67224: Show source lines in tracebacks when using the -c option when running Python #111200
• gh-67224: Make linecache imports relative to improve startup speed #117501

[Arfrever]

When 'python -c ${command}' is used and exception other than SyntaxError occurs, then line causing exception is not shown.

Problem seen in output of last 2 commands below:

$ cat /tmp/test1
1 /
$ cat /tmp/test2
1 / 0
$ cat /tmp/test3
a
$ python3.5 /tmp/test1
  File "/tmp/test1", line 1
    1 /
      ^
SyntaxError: invalid syntax
$ python3.5 /tmp/test2
Traceback (most recent call last):
  File "/tmp/test2", line 1, in <module>
    1 / 0
ZeroDivisionError: division by zero
$ python3.5 /tmp/test3
Traceback (most recent call last):
  File "/tmp/test3", line 1, in <module>
    a
NameError: name 'a' is not defined
$ python3.5 -c '1 /'
  File "<string>", line 1
    1 /
      ^
SyntaxError: invalid syntax
$ python3.5 -c '1 / 0'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ZeroDivisionError: division by zero
$ python3.5 -c 'a'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'a' is not defined

[vstinner]

SyntaxError exceptions have a text attribute which contains the line where the error occurred. It's really a special case. For other exceptions, Python only knows that the error occurred in the file called "<string>".

Being able to display the line for any exception requires a complex development. I'm not interested to implement it, I don't think that it's very useful (compared to the time needed to develop it).

[Arfrever]

It should not be more complex to read a line from a command line argument than to read a line from a regular file.

[terryjreedy]

Code entered with -c seems to be treated the same as code entered at the >>> prompt of the interactive interpreter.

>>> 1/0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

In both cases, the offending code is right there to be seen, so I can understand reluctance to echo it. For SyntaxErrors (and only them) echoing the code is needed to have something to point to.

Idle's Shell does what you want.
>>> 1/0
Traceback (most recent call last):
  File "<pyshell#12>", line 1, in <module>
    1/0
ZeroDivisionError: division by zero

Shell can do this because it has easy, platform-independent access to the tkinter Text widget storing and displaying previously entered code. I presume accessing a system-dependent console history buffer is much harder.

Where the difference really matters is when the error is in previously defined objects.

>>> def f():
...   return a

>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in f
NameError: name 'a' is not defined

versus (Shell)

>>> def f():
	return a

>>> f()
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    f()
  File "<pyshell#15>", line 2, in f
    return a
NameError: name 'a' is not defined

[Arfrever]

Argument of -c option can have multiple lines, while only 1 line can be directly entered in interactive interpreter.

python -c $'line1\nline2\nline3\nline4\n...'

[terryjreedy]

One can paste multiple lines, comprising multiple statements, into the console interprer. (Shell only recognizes a single pasted statement.)
I agree, however, that it seems that Python could keep the split version of the input line for the purpose of tracebacks. I just tried

C:\Users\Terry>python -c "import sys; print(sys.argv)"
['-c']

I expected to see to see a list of 3 strings, not 1.

[Arfrever]

Arguments after argument of -c option are included in sys.argv:

$ python -c "import sys; print(sys.argv)" a b
['-c', 'a', 'b']

[iritkatriel]

CC @pablogsal