[issue34013] Inconsistent SyntaxError for print

[Terry J. Reedy]

Terry J. Reedy  added the comment:

I think that this was properly closed after the last fix.  There are multiple 
issues at play:

1. These parts of the Zen:
"Special cases aren't special enough to break the rules.
Although practicality beats purity.
...
In the face of ambiguity, refuse the temptation to guess."

2. The fact that a parser only reads and checks *python* syntax, while we 
humans have to make a special effort to avoid semantics.  The latter is 
especially true when the semantic is a special-case computing trope. Even if an 
identifier is semantically recognized as a function, its signature (call 
syntax) is specific to the function and is not part of python syntax.

3. The that with PEG parsing, there is no exact failure point. (Pablo just 
documented the PEG parser.  But, Pablo, where is it?  Not in HOWTO or index.)  
This is especially true when there are multiple errors, as in Andre's example.

As long as we only had one special case hint, which depended on the semantic 
knowledge that 'print' is almost certainly meant to mean print with the builtin 
function with a known call syntax, it was fairly easy to get the hint right, 
and in 3.11 we still have

>>> print """jsfl sf
... sjflsfj l
... sjflsjf
... sjfs fj
... sjlsfjlsjg
... """
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?

But we now have more hints, and "print Hello world!" is syntactically the same 
as "a b c!", which gives the same error message.  Even if the first identifier 
is recognized as a function, and parenthesis are added, the result would be 
syntactically identical to "print(b c!)".  At this  point, it is syntactically 
ambiguous whether the fixed argument should be a string "'b c!'" or comma list 
"b, c".  Both are possible for print, but not all functions.  The 'correct' fix 
on only 'obvious' when we add knowledge of the semantics 'Hello, 'world', and 
'!' and the history of their concatenation, 'Hello world!' (but sometimes 
without '!' or capitalization, or with  replacing 'world'), in computing, 
and especially in the teaching of beginners in a particular language.

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

If we change the priority of the error messages, which is unclear if is easily 
possible, the error will suggest that

print hello should be parenthesized as print (hello) Which if corrected will 
leave the "world" part out as a call followed to a name, and here the comma 
suggestion is a valid concern.

I understand the willingness to have a better error here, but I am not sure 
what we can improve here.

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[issue34013] Inconsistent SyntaxError for print

[Andre Roberge]

Andre Roberge  added the comment:

Python 3.10.0rc1 ...

>>> print hello world!
  File "", line 1
print hello world!
  ^^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?

The hint given is not exactly helpful ...

(This example was in a discussion on Twitter 
https://twitter.com/cfbolz/status/1425036431974715400 about a previous handling 
of this invalid syntax case where it was mentioned that pypy verifies that the 
suggestion it makes actually yields syntactically valid code.)

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[issue34013] Inconsistent SyntaxError for print

[miss-islington]

miss-islington  added the comment:


New changeset 35035bc35a9cb8617ab9fe9aac38aaf67c926aef by Miss Islington (bot) 
in branch '3.10':
bpo-34013: Don't consider a grouped expression when reporting legacy print 
syntax errors (GH-27521)
https://github.com/python/cpython/commit/35035bc35a9cb8617ab9fe9aac38aaf67c926aef


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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue34013] Inconsistent SyntaxError for print

[miss-islington]

Change by miss-islington :


--
pull_requests: +26037
pull_request: https://github.com/python/cpython/pull/27522

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:


New changeset 208a7e957b812ad3b3733791845447677a704f3e by Pablo Galindo Salgado 
in branch 'main':
bpo-34013: Don't consider a grouped expression when reporting legacy print 
syntax errors (GH-27521)
https://github.com/python/cpython/commit/208a7e957b812ad3b3733791845447677a704f3e


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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
pull_requests: +26036
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/27521

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

Is not about the eagerness, the problem is that it matches *first*, the parser 
never gets to the indentation error in the second phase.

For example, with:

print(3) $ 34

❯ ./python bug.py
  File "/home/pablogsal/github/python/main/bug.py", line 1
print(3) $ 34
^^^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?

The problem is that is matching the (3) as print + a number between 
parentheses. We just need to disallow to continue matching on the right
if it finds a '('.

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[issue34013] Inconsistent SyntaxError for print

[Brandt Bucher]

Brandt Bucher  added the comment:

Reopening as a release blocker.

It appears that this new rule is far too eager, and matches a much wider range 
of inputs than intended. Here is a case where it changes an IndentationError 
into a SyntaxError:

$ cat bug.py
print()
boom

On 3.9 (correct):

$ ./python.exe --version
Python 3.9.6+
$ ./python.exe bug.py
  File "/Users/brandtbucher/Desktop/GitHub/cpython/bug.py", line 2
boom
IndentationError: unexpected indent

On 3.10 (incorrect):

$ ./python.exe --version
Python 3.10.0b4+
$ ./python.exe bug.py
  File "/Users/brandtbucher/Desktop/GitHub/cpython/bug.py", line 1
print()
^^^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?

On 3.11 (incorrect):

$ ./python.exe --version
Python 3.11.0a0
$ ./python.exe bug.py
  File "/Users/brandtbucher/Desktop/GitHub/cpython/bug.py", line 1
print()
^^^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?

I recommend that this either be fixed or reverted before the RC.

--
components: +Parser -Interpreter Core
nosy: +brandtbucher
priority: normal -> release blocker
resolution: fixed -> 
stage: resolved -> needs patch
status: closed -> open
type: enhancement -> behavior

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue34013] Inconsistent SyntaxError for print

[miss-islington]

miss-islington  added the comment:


New changeset 68e3dca0687c4c8e61ed98aed82f81049880c0ce by Miss Islington (bot) 
in branch '3.10':
bpo-34013: Move the Python 2 hints from the exception constructor to the parser 
(GH-27392)
https://github.com/python/cpython/commit/68e3dca0687c4c8e61ed98aed82f81049880c0ce


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[issue34013] Inconsistent SyntaxError for print

[miss-islington]

Change by miss-islington :


--
nosy: +miss-islington
nosy_count: 15.0 -> 16.0
pull_requests: +25926
pull_request: https://github.com/python/cpython/pull/27393

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:


New changeset ecc3c8e4216958d85385bf2467441c975128f26c by Pablo Galindo Salgado 
in branch 'main':
bpo-34013: Move the Python 2 hints from the exception constructor to the parser 
(GH-27392)
https://github.com/python/cpython/commit/ecc3c8e4216958d85385bf2467441c975128f26c


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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:


New changeset b977f8510e2ff4f11e3bda920722098a242fc8cc by Pablo Galindo Salgado 
in branch '3.10':
[3.10] bpo-34013: Generalize the invalid legacy statement error message 
(GH-27389). (GH-27391)
https://github.com/python/cpython/commit/b977f8510e2ff4f11e3bda920722098a242fc8cc


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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
pull_requests: +25925
pull_request: https://github.com/python/cpython/pull/27392

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
pull_requests: +25924
pull_request: https://github.com/python/cpython/pull/27391

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:


New changeset 6948964ecf94e858448dd28eea634317226d2913 by Pablo Galindo Salgado 
in branch 'main':
bpo-34013: Generalize the invalid legacy statement error message (GH-27389)
https://github.com/python/cpython/commit/6948964ecf94e858448dd28eea634317226d2913


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[issue34013] Inconsistent SyntaxError for print

[Ammar Askar]

Change by Ammar Askar :


--
pull_requests: +25923
pull_request: https://github.com/python/cpython/pull/27390

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
keywords: +patch
pull_requests: +25921
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/27389

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[issue34013] Inconsistent SyntaxError for print

[Irit Katriel]

Irit Katriel  added the comment:

This case has changed recently, and not for the better:

>>> print f(3)
  File "", line 1
print f(3)
^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?

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[issue34013] Inconsistent SyntaxError for print

[Lysandros Nikolaou]

Change by Lysandros Nikolaou :


--
nosy: +lys.nikolaou

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[issue34013] Inconsistent SyntaxError for print

[Andre Roberge]

Andre Roberge  added the comment:

+1 to the idea of adding something to the grammar, and have a simple error 
message:

SyntaxError: Missing parentheses in call to 'print'.

in *all* cases, including the first one that prompted this bug report.

I write that even though I have created a third-party package based on the idea 
that beginners (and sometimes others...) might benefit from a more detailed 
error message (which is taken care of already by friendly-traceback).

--
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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

Let's step back a bit and focus on the issue at hand. The problem is the 
following:

* We **already** have a warning for the print statement without parens:

Python 3.9.1 (default, Dec 14 2020, 11:49:16)
[Clang 12.0.0 (clang-1200.0.32.27)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> print x
  File "", line 1
print x
  ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(x)?

This is achieved by inspecting the syntax error and checking some conditions, 
which I personally find it uglier than a resilient grammar rule.

* The question is if we want to make the rule more resilient or delete it 
whatsoever. The status quo doesn't seem like a good fit

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[issue34013] Inconsistent SyntaxError for print

[Vedran Čačić]

Vedran Čačić  added the comment:

> "It's still one of the most common beginner mistakes"

Do you have any data to back this up? I really think it's overblown.

On the other hand, if it really _is_ so, how about changing the language? It 
wouldn't be the first thing that was changed for Py3, and then changed back 
once people realized the old way was better.

It seems to me totally backwards to have a construct in the grammar, only to 
report it as an error. "I understand you, but you still have to use _this_ way 
to write what you want." I really think Python shouldn't be that kind of 
language.

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[issue34013] Inconsistent SyntaxError for print

[Irit Katriel]

Irit Katriel  added the comment:

I agree with Terry’s point about printing long expressions in the error msg. 
Perhaps just the preamble would be useful though:

SyntaxError: Missing parentheses in call to 'print'. 

Instead of just

SyntaxError: invalid syntax.

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[issue34013] Inconsistent SyntaxError for print

[Terry J. Reedy]

Terry J. Reedy  added the comment:

'Consistency' is in the eye of the beholder in that it is relative to some 
ideal.  'Inconsistent' has too much baggage as bad'.  I would prefer to call 
the current rule 'restricted' or 'limited' and judge any expansion on its own 
merits.

The arguments to print can take an unbounded amount of space.  So a general 
message "Did you mean print()?" could also be indefinitely 
long.  I don't think this is a good idea.  Of course, the same applies to a 
single literal, especially multiline string literals.  But at least the latter 
are currently clipped to only the first line in the message.

>>> print '''first line
second line'''
SyntaxError: Missing parentheses in call to 'print'. Did you mean 
print('''first line)?

(The above would be better with trailing ... .) This abbreviation would be 
harder with multiple arguments.  The special message is for beginners.  They 
might print a literal or name without ()s more frequently.  I not sure that 
they need the reminder with every mistake.

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[issue34013] Inconsistent SyntaxError for print

[Ammar Askar]

Ammar Askar  added the comment:

It's still one of the most common beginner mistakes, personally I think the 
trade-off in complexity at least for the grammar level fix is worth it here.

--
nosy: +ammar2

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[issue34013] Inconsistent SyntaxError for print

[Vedran Čačić]

Vedran Čačić  added the comment:

Aren't we overthinking this? Python 2 is a dead language. It has reached end of 
life more than a year ago (and was scheduled to do so in 2015). Why are we 
still trying to accomodate something that stopped being relevant a long time 
ago?

--
nosy: +veky

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[issue34013] Inconsistent SyntaxError for print

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

> Would it be too much if add a Python 2 rule for print statement in grammar to 
> produce better error message?

Please, go ahead. I think it makes sense and with our latest change in the 
parser, such new error message will have no impact on performance whatsoever. 
Please, at me as a reviewer :)

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[issue34013] Inconsistent SyntaxError for print

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Would it be too much if add a Python 2 rule for print statement in grammar to 
produce better error message?

invalid_print_stmt:
| 'print' ( test (',' test)* [','] ] |
'>>' test [ (',' test)+ [','] ) {
  RAISE_INVALID_PRINT_STATEMENT() }

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nosy: +pablogsal

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[issue34013] Inconsistent SyntaxError for print

[Irit Katriel]

Irit Katriel  added the comment:

Still the same in 3.10:

Python 3.10.0a5+ (heads/master:bf2e7e55d7, Feb 11 2021, 23:09:25) [MSC v.1928 
64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print 3
  File "", line 1
print 3
  ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(3)?
>>> def f(x): return x
...
>>> print f(3)
  File "", line 1
print f(3)
  ^
SyntaxError: invalid syntax

--
nosy: +iritkatriel
versions: +Python 3.10 -Python 3.8

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[issue34013] Inconsistent SyntaxError for print

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

See also #32685.

--
nosy: +CuriousLearner, nitishch

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[issue34013] Inconsistent SyntaxError for print

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Eric, Nick, Serhiy: this issue proposes to extend the print message patch of 
#30597 to cover more cases.  On the face of it, this seems sensible, but I have 
no read the original discussion or the current and proposed patches.

--
nosy: +eric.smith, ncoghlan, serhiy.storchaka, terry.reedy

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[issue34013] Inconsistent SyntaxError for print

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

@corona10 You might want to discuss this at 
https://mail.python.org/pipermail/python-ideas/ so that you get some initial 
feedback on the work and it's acceptance to the core.

Thanks

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[issue34013] Inconsistent SyntaxError for print

[Dong-hee Na]

Dong-hee Na  added the comment:

And here's my work in progress patch.

https://github.com/corona10/cpython/commit/133825346fd60e518e9ab5830a0755250c8c3e79

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[issue34013] Inconsistent SyntaxError for print

[Dong-hee Na]

Dong-hee Na  added the comment:

Thanks,

my easy patch is worked by pre-checking left paren index. but some edge case 
which I don't expect should be considered.

 if (left_paren_index != -1) {
-/* Use default error message for any line with an opening paren */
-return 0;
+   int found_white_space = 0;
+   int found_other_char = 0;
+   Py_ssize_t pos = 0;
+   while(pos != left_paren_index) {
+   int kind = PyUnicode_KIND(self->text);
+   void *data = PyUnicode_DATA(self->text);
+Py_UCS4 ch = PyUnicode_READ(kind, data, pos);
+   if (Py_UNICODE_ISSPACE(ch)) {
+found_white_space = 1;
+   }
+   if (!Py_UNICODE_ISSPACE(ch) && found_white_space == 1) {
+found_other_char = 1;
+   }
+   pos++;
+   }
+
+   if (found_other_char == 0) {
+   return 0;
+   }
 }


Type "help", "copyright", "credits" or "license" for more information.
>>> print (foo.)
  File "", line 1
print (foo.)
   ^
SyntaxError: invalid syntax

>>> print "a".toupper().tolower()
  File "", line 1
print "a".toupper().tolower()
^
SyntaxError: Missing parentheses in call to 'print'. Did you mean 
print("a".toupper().tolower())?

SyntaxError: Missing parentheses in call to 'print'. Did you mean 
print(Foo().header(a=foo(1)))?

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[issue34013] Inconsistent SyntaxError for print

[Dong-hee Na]

Dong-hee Na  added the comment:

>>> class Foo:
... pass
...
>>> print Foo().header(a=foo(1))
  File "", line 1
print Foo().header(a=foo(1))
^
SyntaxError: Missing parentheses in call to 'print'. Did you mean 
print(Foo().header(a=foo(1)))?

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[issue34013] Inconsistent SyntaxError for print

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

I took an initial stab at this and there is a comment where if there is an open 
paren then to use the normal error message. Additional context on the issue 
which lists false positive cases where the change was introduced 
https://bugs.python.org/issue21669. I removed the check where the left paren 
count is not -1 in case of a function call and it seems to work. Of course, 
there are cases to handle as mentioned in the linked issue and I tried some of 
the cases like "foo".toupper().tolower() and the results as below : 

Patch : 

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index bb50c1c..7e616cf 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2966,10 +2966,7 @@ _report_missing_parentheses(PySyntaxErrorObject *self)
 if (left_paren_index < -1) {
 return -1;
 }
-if (left_paren_index != -1) {
-/* Use default error message for any line with an opening paren */
-return 0;
-}
+
 /* Handle the simple statement case */
 legacy_check_result = _check_for_legacy_statements(self, 0);
 if (legacy_check_result < 0) {

Cases :

➜  cpython git:(master) ✗ cat foo_print.py
class Foo:
pass

print Foo().header(a=foo(1))
➜  cpython git:(master) ✗ ./python foo_print.py
  File "foo_print.py", line 4
print Foo().header(a=foo(1))
^
SyntaxError: Missing parentheses in call to 'print'. Did you mean 
print(Foo().header(a=foo(1)))?

➜  cpython git:(master) ✗ cat foo_print.py
print "a".toupper().tolower()
➜  cpython git:(master) ✗ ./python foo_print.py
  File "foo_print.py", line 1
print "a".toupper().tolower()
^
SyntaxError: Missing parentheses in call to 'print'. Did you mean 
print("a".toupper().tolower())?


Linked cases in the patch : 

➜  cpython git:(master) ✗ cat foo_print.py
print (foo.)
➜  cpython git:(master) ✗ ./python foo_print.py
  File "foo_print.py", line 1
print (foo.)
   ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print((foo.))?


Would like to link to https://hackmd.io/s/ByMHBMjFe#08-Debugging-Python-Objects 
. As a beginner the tutorial was helpful and I had to set a break point on 
Objects/exceptions.c:1323 where SyntaxError_init is called and then execute 
line by line where the current code returns the left_paren_index which you can 
set as `set left_paren_index = -1` to skip the branch and then continue the 
program to print the above error messages. IMO I think it was an explicit 
decision with this change being done 4 years ago with the false positive cases 
and tests listed but I am curious if there are any improvements in this area to 
be done.


Thanks

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[issue34013] Inconsistent SyntaxError for print

[Piyush Hajare]

Piyush Hajare <4piyushhaj...@gmail.com> added the comment:

I'm interested to solve this issue

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nosy: +piyushhajare

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[issue34013] Inconsistent SyntaxError for print

[Dong-hee Na]

Dong-hee Na  added the comment:

@xtreak

Thanks, I have interest with this issue :)
I will take a look at the implementation

Thanks!

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[issue34013] Inconsistent SyntaxError for print

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

Related issue that introduced the error message if you would like to take a 
look at the implementation : https://bugs.python.org/issue30597

Thanks

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[issue34013] Inconsistent SyntaxError for print

[Dong-hee Na]

Change by Dong-hee Na :


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components: +Interpreter Core
type:  -> enhancement

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[issue34013] Inconsistent SyntaxError for print

[Dong-hee Na]

New submission from Dong-hee Na :

Python 3.8.0a0 (heads/master-dirty:0cdf5f4289, Jul  1 2018, 02:30:31)
[Clang 9.1.0 (clang-902.0.39.1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> print "hi"
  File "", line 1
print "hi"
 ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print("hi")?
>>> def add(a,b):
... return a + b
...
>>> print add(3,5)
  File "", line 1
print add(3,5)
^
SyntaxError: invalid syntax

IMHO, an error message should be 'SyntaxError: Missing parentheses in call to 
'print'. Did you mean print(add(3,5))?' but it is not.

--
messages: 320797
nosy: corona10
priority: normal
severity: normal
status: open
title: Inconsistent SyntaxError for print
versions: Python 3.8

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