Scope#
When you type a name its definition (and therefore its meaning and usage) as used by the Python interpreter depends on where it is defined.
In Python, a variable is only available from inside the region it is created. This is called scope. There are five different scopes:
- local scope: names defined inside a function (or lambda)
- enclosing scope: names in the local scope of enclosing functions (nested functions)
- global scope: names defined at the top level of a module (or declared global with the global keyword)
- built-in: reserved names preassigned by Python (e.g., import, def, for)
Contents
Local Scope#
These are names defined inside a function or method.
local_scope.py # example of local scope def local_example(): # define a variable 'x' whose scope is local to the function x = "I'm local" print(x) # if we call local_example() the result will print "I'm local". local_example() # the following would result in an error, as x is not defined outside the function print(x)Enclosing Scope#
These are names defined in the local scope of an enclosing function.
If you only ever expect to use a function within an existing function, yes, you can define a function within another function. This is called a nested function. The scope of names is therefore determined by where they are defined.
enclosing_scope.py # example of enclosing scope def outer(): # we define a variable 'x' within the scope of the outer() function x = "I'm in the enclosing scope" def inner(): print(x) # accesses x from enclosing function # if the outer() function is called, inner() is called too inner() # we call the outer() function outer()Global Scope#
These are names defined at the top level (i.e., starting at column 0) of a module, or declared global with the global keyword.
global_scope.py # example of global scope x = "I'm global" def show_global(): print(x) # read-only access to the global value of x show_global()If you want to be able to modify a global variable, you can use the global keyword.
This is a safety feature so that you don't accidentally modify a global variable within a non-global scope unless you explicitly use the global keyword.
global_keyword.py # example of the global keyword # we define a global variable called 'count' count = 0 def increment_by_2(): global count # we use the 'global' keyword so we can modify x count += 2 # we call the increment_by_2() function inside a for loop for i in range(0,5): increment_by_2() print("i={}; count: {}".format(i, count))When this code is executed, we can see the value of i being incremented by the for loop, as well as the value of the global variable count being incremented within the increment_by_2() function.
/pyboard> repl Entering REPL. Use Control-X to exit. > MicroPython v1.25.0 on 2025-04-15; Raspberry Pi Pico with RP2040 Type "help()" for more information. >>> >>> import global_keyword i=0; count: 2 i=1; count: 4 i=2; count: 6 i=3; count: 8 i=4; count: 10 >>>
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