I'm having some trouble understanding how Python handles variables
across multiple modules. I've dug through the documentation, but I
still find myself at a loss.
When you import a module, are you creating an instance of the
variables within? For instance, if I have one file, "variables.py",
which contains "myvar = 0", and I import it into both "foo.py" and
"bar.py" with the line "from variables import *", and then set myvar
in "foo.py" and "bar.py" to different values, will each file have a
different value for myvar? If so, how can I ensure that a change to
myvar in "bar.py" is reflected by "foo.py"? Or am I completely off
base? 5 1287
Aaron Scott schrieb:
I'm having some trouble understanding how Python handles variables
across multiple modules. I've dug through the documentation, but I
still find myself at a loss.
When you import a module, are you creating an instance of the
variables within? For instance, if I have one file, "variables.py",
which contains "myvar = 0", and I import it into both "foo.py" and
"bar.py" with the line "from variables import *", and then set myvar
in "foo.py" and "bar.py" to different values, will each file have a
different value for myvar? If so, how can I ensure that a change to
myvar in "bar.py" is reflected by "foo.py"? Or am I completely off
base?
Just wirte test code ! Python is cool for checking such things, you do
do
not have to compile, you need not write boilerplate main() stuff.
Greetings, Uwe
Just wirte test code !
variables.py:
myvar = 5
print myvar
foo.py:
from variables import *
def PrintVar():
print myvar
bar.py:
from variables import *
from foo import *
print myvar
myvar = 2
print myvar
PrintVar()
"python bar.py" output:
5
5
2
5
.... which is what I was expecting, but not what I want. Obviously,
each import is creating its own instance of the variable. What I need
is a way to change myvar from within "bar.py" so that PrintVar()
returns the new value, even though it's in a different module.
On Wed, Jul 23, 2008 at 3:06 PM, Aaron Scott
<aa***************@gmail.comwrote:
... which is what I was expecting, but not what I want. Obviously,
each import is creating its own instance of the variable. What I need
is a way to change myvar from within "bar.py" so that PrintVar()
returns the new value, even though it's in a different module.
That's what happens when you do "from variables import *", it creates
those names in the local namespace. If you just import the module,
then you can do what you want. For example:
---variables.py---
myvar = 5
print myvar
---foo.py---
import variables
def PrintVar():
print variables.myvar
---bar.py---
import variables, foo
print variables.myvar
variables.myvar = 2
print variables.myvar
foo.PrintVar()
---output from running bar.py---
5
5
2
2
For more on how the import statement works, see the library reference
( http://docs.python.org/ref/import.html), or maybe this article on the
various ways you can import things and the differences between them
( http://effbot.org/zone/import-confusion.htm)
--
Jerry
Aaron Scott wrote:
I'm having some trouble understanding how Python handles variables
across multiple modules. I've dug through the documentation, but I
still find myself at a loss.
When you import a module, are you creating an instance of the
variables within? For instance, if I have one file, "variables.py",
which contains "myvar = 0", and I import it into both "foo.py" and
"bar.py" with the line "from variables import *", and then set myvar
in "foo.py" and "bar.py" to different values, will each file have a
different value for myvar? If so, how can I ensure that a change to
myvar in "bar.py" is reflected by "foo.py"? Or am I completely off
base?
first read this to learn how objects and variables work in Python: http://effbot.org/zone/python-objects.htm
and then read this to learn how from-import works, and when you're
supposed to use it: http://effbot.org/zone/import-confusion.htm
hope this helps!
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