[issue14049] execfile() fails on files that use global variables inside functions

[Terry J. Reedy]

Terry J. Reedy tjre...@udel.edu added the comment:

Searching on 'exec NameError' shows that this issue is a duplicate of (behavior 
issue) #1167300 which contained an essentially identical example

 exec \
... x = 3
... def f():
... print x
... f()
...  in {}, {}

#1167300 was closed as a duplicate of (behavior issue) #991196, which in turn 
was closed as 'won't fix' (ie, works as it must). Doc issue #4831, which 
resulted in some doc changes, seems related to this but is not the same. I 
believe this issue is a duplicate of #13557, which has a patch. I will add my 
proposed change there.

Anyway, my comments:

In 3.2.2, this runs

#prog='''\
x = 1
def weird():
y = x + 1
return y
print(weird())
#'''
#exec(prog)

The same uncommented does also, as does adding ',{}' to the call.
Adding ',{},{}' gives the NameError.
With one named {} arg passed twice, as follows, it runs.

d = {}
exec(prog, d, d)

The reasons for these results are:
1. assignments are *always* to the local namespace.
2. normally, for module code, the local and global namespaces are the same.
3. in the example, 'x=1' is the same as values['x']=1, while within the 
function, 'y=x+1' looks up x in gvalues.

This is the same explanation as given in #1167300.

--
nosy: +terry.reedy
resolution:  - duplicate
status: open - closed
superseder:  - exec of list comprehension fails on NameError
versions: +Python 3.2, Python 3.3

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[issue14049] execfile() fails on files that use global variables inside functions

[anatoly techtonik]

New submission from anatoly techtonik techto...@gmail.com:

main.py below fails to execute local.py, which work ok (outputs '2') when 
processed directly in console.

Docs are not explaining anything. They spread fear and uncertainty around 
locals, but nothing is said why globals may fail.
http://docs.python.org/library/functions.html#execfile


---[cut main.py]---
values = {}
glavues = {}
execfile('local.py', glavues, values)
---[/cut]---

---[cut local.py]---
x = 1
def weird():
y = x + 1
return y
print weird()
---[/cut]---



Traceback (most recent call last):
  File main.py, line 5, in module
execfile('local.py', glavues, values)
  File local.py, line 7, in module
print weird()
  File local.py, line 5, in weird
y = x + 1
NameError: global name 'x' is not defined

--
assignee: docs@python
components: Documentation, Library (Lib)
messages: 153643
nosy: docs@python, techtonik
priority: normal
severity: normal
status: open
title: execfile() fails on files that use global variables inside functions
versions: Python 2.7

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