# Reading and writing a global variable
**URL:** https://discourse.julialang.org/t/reading-and-writing-a-global-variable/121996
**Category:** New to Julia
**Created:** [October 30, 2024, 2:45pm UTC](https://discourse.julialang.org/t/reading-and-writing-a-global-variable/121996 "2024-10-30T14:45:23Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Matthijs\_1971](https://discourse.julialang.org/u/Matthijs_1971)
#### Post date: [October 30, 2024, 2:45pm UTC](https://discourse.julialang.org/t/reading-and-writing-a-global-variable/121996/1 "2024-10-30T14:45:23Z")
Please consider the following code:
```julia
module MyModule
global MY_GLOBAL = 42
function test()::Nothing
println("MY_GLOBAL ", MY_GLOBAL)
# MY_GLOBAL = 3
return nothing
end
end # MyModule
MyModule.test()
```
As is, this code just runs and `MY_GLOBAL` is in scope for reading. Now if the line `MY_GLOBAL = 3` is commented back in, the script fails on the line with the `println` call - which it could execute before. The error is _ERROR: LoadError: UndefVarError: `MY_GLOBAL` not defined_. Of course, adding `global MY_GLOBAL` in the function makes the code run, but that is not the point. IMHO, a variable is in scope in a function or not and that should not depend on read or write attempts. What is going on?
---
### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [October 30, 2024, 3:03pm UTC](https://discourse.julialang.org/t/reading-and-writing-a-global-variable/121996/2 "2024-10-30T15:03:33Z")
Inside a function scope, Julia first looks for all new assignments.
If an there is an assignment which shares the same name as a global variable, it treats _all_ references to that variable as local, even ones that happen before the assignment.
This creates somewhat confusing errors, for sure.
---
### Author:  [@bertschi](https://discourse.julialang.org/u/bertschi)
#### Post date: [October 30, 2024, 4:50pm UTC](https://discourse.julialang.org/t/reading-and-writing-a-global-variable/121996/3 "2024-10-30T16:50:24Z")
Just for the record, Python works exactly the same in this case:
```python
my_global = 42
def fun():
print(my_global)
# Fails if line below is uncommented
# my_global = 3
fun()
```