[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:


New changeset de2aea0ff02fa9486365ce9d215bef150fae3a0b by Pablo Galindo in 
branch 'master':
bpo-34939: Allow annotated global names in module namespace (GH-9844)
https://github.com/python/cpython/commit/de2aea0ff02fa9486365ce9d215bef150fae3a0b


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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


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pull_requests: +9217
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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

I think we can just go ahead and allow this. If there is a volunteer, please go 
ahead, otherwise I will try to find time for this myself.

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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Rohan Padhye]

Rohan Padhye  added the comment:

Another point I'd like to make is that there is no error in either file or 
interactive if the annotated assignment appears before the `global` declaration 
like so:

```
x:int = 0

def set_x():
global x
x = 1

# Works fine!
```

The syntax error specifically occurs when the annotated assignment occurs after 
a `global` declaration in the program, even if the assignment is in a different 
scope.

Neither the docs nor the PEP say anything about such an ordering constraint.

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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

This looks similar to say

x = 1
global x

It is an error in a file, but is not an error in interactive mode.

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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Guido van Rossum]

Guido van Rossum  added the comment:

I agree with Ivan.

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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

Hm, I think this should be allowed. The formulation in the docs is not very 
clear, but the wording in the PEP clarifies the intention. Indeed, only 
annotations at the same scope with global declarations should be prohibited.

So I think this is a bug.

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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

The error message was added with 6cff8744a0ae58c88728df8bbca4580ffa6c6a86 and 
issue27999. The docs were also changed as below with the commit : 

https://docs.python.org/3.8/reference/simple_stmts.html#the-global-statement

> Names listed in a global statement must not be defined as formal parameters 
> or in a for loop control target, class definition, function definition, 
> import statement, or variable annotation.


Thanks

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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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[issue34939] Possibly spurious SyntaxError: annotated name can't be global

[Rohan Padhye]

New submission from Rohan Padhye :

The following code when run as a script file gives syntax error:

```
def set_x():
global x
x = 1

x:int = 0   # SyntaxError: annotated name 'x' can't be global
```

PEP 526 does not seem to forbid this. The error message "annotated name [...] 
can't be global" is usually seen when using the `global x` declaration *in the 
same scope* as an annotated assignment. In the above case, the annotated 
assignment is outside the function scope, yet Python 3.7 gives a syntax error.


Is this a bug in CPython? Or should the PEP 526 document say something about 
forward references?

Interestingly, if the above program is run in interactive mode, there is no 
syntax error. 

In interactive mode:
```
>>> def set_x():
... global x
... x = 1
... 
>>> x:int = 0
>>> set_x()
>>> print(x)
1
```

Further, forward references work fine with `nonlocal`. For example, the 
following works fine both as a script file and in interactive mode:
```
def outer():
def inner():
nonlocal y
y = 1
y:int = 0
```

I don't see why a forward reference in `global` is a problem.

--
components: Interpreter Core
messages: 327378
nosy: rohanpadhye
priority: normal
severity: normal
status: open
title: Possibly spurious SyntaxError: annotated name can't be global
type: behavior
versions: Python 3.7

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