Python Scope
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Scope
A variable is only available from inside the region it is
created. This is called scope.
Local Scope
A variable created inside a function belongs to the local scope of
that function, and can only be used inside that function.
Example
A variable created inside a function is available inside that function:
def myfunc():
x = 300
print(x)
myfunc()
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Function Inside Function
As explained in the example above, the variable x is not available outside the function,
but it is available for any function inside the function:
Example
The local variable can be accessed from a function within the function:
def myfunc():
x = 300
def myinnerfunc():
print(x)
myinnerfunc()
myfunc()
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Global Scope
A variable created in the main body of the Python code is a global variable
and belongs to the global scope.
Global variables are available from within any scope, global and local.
Example
A variable created outside of a function is global and can be used by
anyone:
x = 300
def myfunc():
print(x)
myfunc()
print(x)
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Naming Variables
If you operate with the same variable name inside and outside of a function, Python will treat them as two
separate variables,
one available in the global scope (outside the function) and one available in the local scope (inside the function):
Example
The function will print the local x, and
then the code will print the global x:
x = 300
def myfunc():
x = 200
print(x)
myfunc()
print(x)
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Global Keyword
If you need to create a global variable, but are stuck in the local scope, you can use the
global keyword.
The global keyword makes the variable global.
Example
If you use the global keyword, the variable belongs to the global scope:
def myfunc():
global x
x = 300
myfunc()
print(x)
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Also, use the global keyword if you want to
make a change to a global variable inside a function.
Example
To change the value of a global variable inside a function, refer to the
variable by using the global keyword:
x = 300
def myfunc():
global x
x = 200
myfunc()
print(x)
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Nonlocal Keyword
The nonlocal keyword is used to work with variables inside nested functions.
The nonlocal keyword makes the variable belong to the outer function.
Example
If you use the nonlocal keyword, the variable will belong to the outer function:
def myfunc1():
x = "Jane"
def myfunc2():
nonlocal x
x = "hello"
myfunc2()
return x
print(myfunc1())
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The LEGB Rule
Python follows the LEGB rule when looking up variable names, and searches for them in this order:
- Local - Inside the current function
- Enclosing - Inside enclosing functions (from inner to outer)
- Global - At the top level of the module
- Built-in - In Python's built-in namespace
Example
Understanding the LEGB rule:
x = "global"
def outer():
x = "enclosing"
def inner():
x = "local"
print("Inner:", x)
inner()
print("Outer:", x)
outer()
print("Global:", x)
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