|  | exec(code) not allowing import on top level? | | |
| | | Peter Teuben |  |
|  Posted: Tue Jul 29, 2008 1:26 am Post subject: exec(code) not allowing import on top level? |  |
if I define a simple string code, with the following contents:
import math
def foo(x):
return math.sqrt(x)
and i run it using exec(code) in python, math is not known. But when I
recode the string as:
def foo(x):
import math
return math.sqrt(x)
it works fine. That seemed like an inconsistency, since it works
fine otherwise, as expected. It's easy to work around, but
just odd to find this out.
thanks
peter |
| |
| | | Gary Herron | |
| | Posted: Tue Jul 29, 2008 2:17 am Post subject: Re: exec(code) not allowing import on top level? | |
Peter Teuben wrote:
| Quote: |
if I define a simple string code, with the following contents:
import math
def foo(x):
return math.sqrt(x)
|
What? You have not told us something important here. First, that code
won't fail because it does not even execute the function foo -- it just
defines it. Second, if I exend your string with one more line
"foo(123)" to actually execute the code, it still works as expected.
So let's try this again... and this time please please also show us the
full text of the error message.
Gary Herron
| Quote: |
and i run it using exec(code) in python, math is not known. But when I
recode the string as:
def foo(x):
import math
return math.sqrt(x)
it works fine. That seemed like an inconsistency, since it works
fine otherwise, as expected. It's easy to work around, but
just odd to find this out.
thanks
peter
--
LINK |
|
| |
| | | Gary Herron | |
| | Posted: Tue Jul 29, 2008 2:18 am Post subject: Re: exec(code) not allowing import on top level? | |
Peter Teuben wrote:
| Quote: |
if I define a simple string code, with the following contents:
import math
def foo(x):
return math.sqrt(x)
|
What? You have not told us something important here. First, that code
won't fail because it does not even execute the function foo -- it just
defines it. Second, if I extended your string with one more line
"foo(123)" to actually execute the code, it still works as expected.
So let's try this again... and this time please please also show us the
full text of the error message.
Gary Herron
| Quote: |
and i run it using exec(code) in python, math is not known. But when I
recode the string as:
def foo(x):
import math
return math.sqrt(x)
it works fine. That seemed like an inconsistency, since it works
fine otherwise, as expected. It's easy to work around, but
just odd to find this out.
thanks
peter
--
LINK |
|
| |
| | | Steven D'Aprano | |
| | Posted: Tue Jul 29, 2008 6:43 am Post subject: Re: exec(code) not allowing import on top level? | |
On Tue, 29 Jul 2008 03:26:45 +0000, Peter Teuben wrote:
| Quote: | if I define a simple string code, with the following contents:
import math
def foo(x):
return math.sqrt(x)
and i run it using exec(code) in python, math is not known.
|
Works for me.
| Quote: | code = """import math
.... def foo(x): |
.... return math.sqrt(x)
.... """
| Quote: |
exec code
foo(25)
5.0 |
By the way, exec is a statement, not a function, so you don't need the
brackets.
--
Steven |
| |
| | | Peter Otten | |
| | Posted: Tue Jul 29, 2008 9:48 am Post subject: Re: exec(code) not allowing import on top level? | |
| |  | |
Peter Teuben wrote:
| Quote: |
if I define a simple string code, with the following contents:
import math
def foo(x):
return math.sqrt(x)
|
The
import math
statement puts 'math' in the local namespace, and foo looks it up in the
global namespace. This can only work when these namespaces are the same:
| Quote: | code = """
.... import math |
.... def foo(x):
.... return math.sqrt(x)
.... print foo(2)
.... """
| Quote: | exec code in {}
1.41421356237
exec code in {}, {}
Traceback (most recent call last): |
File "<stdin>", line 1, in <module>
File "<string>", line 5, in <module>
File "<string>", line 4, in foo
NameError: global name 'math' is not defined
You could argue that Python should always look into the local namespace and
then fall back to the global namespace but that would be fruitless extra
work in most cases. I think it can only hapen with exec/eval, and as you
have seen in the other responses even there it works on the module level
because -- tada!
| Quote: | globals() is locals()
True |
| Quote: | and i run it using exec(code) in python, math is not known. But when I
recode the string as:
def foo(x):
import math
return math.sqrt(x)
|
Here Python "guesses" that math is a local variable and that guess is
correct. If you wrote
import math
def foo(x):
return math.sqrt(x)
math = 42
Python would still guess that math is a local name and you would end up with
a runtime exception.
Peter |
| |
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