
One of the most fundamental concepts in programming is scope — it defines the visibility and lifetime of variables. In Python, understanding how scope works is essential for writing clean, bug-free code.
In this tutorial, we’ll cover:
-
What is scope in Python?
-
The LEGB rule
-
Local, Enclosing, Global, and Built-in scopes
-
The
global
andnonlocal
keywords -
A complete code example
-
Tips and common pitfalls
What is Scope?
Scope refers to the region of a Python program where a particular variable is accessible. Python has several levels of scope that determine which variable names are visible and when.
The LEGB Rule
Python resolves variables using the LEGB rule, which stands for:
-
Local
-
Enclosing
-
Global
-
Built-in
Python checks for a variable name in this order.
1️⃣ Local Scope
Variables defined inside a function are in the local scope.
def my_function():
x = 10 # Local variable
print(x)
my_function() # Output: 10
# print(x) # Error: x is not defined (outside the local scope)
2️⃣ Enclosing Scope
This applies to nested functions. The inner function can access variables from the outer (enclosing) function.
def outer():
a = "outer"
def inner():
print(a) # Accessing enclosing variable
inner()
outer() # Output: outer
3️⃣ Global Scope
Variables defined at the top level of a script or module are in the global scope.
x = "global"
def show():
print(x)
show() # Output: global
4️⃣ Built-in Scope
These are names preassigned by Python. You can see them with dir(__builtins__)
.
print(len("Hello")) # 'len' is a built-in function
The global
Keyword
Use global
to modify a global variable inside a function.
Example:
count = 0
def increment():
global count
count += 1
increment()
print(count) # Output: 1
⚠️ Without global
, the above will raise an UnboundLocalError
.
The nonlocal
Keyword
Use nonlocal
to modify a variable in the enclosing (non-global) scope.
Example:
def outer():
num = 10
def inner():
nonlocal num
num += 5
print("Inner:", num)
inner()
print("Outer:", num)
outer()
# Output:
# Inner: 15
# Outer: 15
Complete Example: Scope in Action
x = "global"
def outer():
x = "enclosing"
def inner():
x = "local"
print("Inner:", x) # local scope
inner()
print("Outer:", x) # enclosing scope
outer()
print("Global:", x) # global scope
Output:
Inner: local
Outer: enclosing
Global: global
Tips for Mastering Scope
-
✅ Use local variables by default — they’re safer and more predictable.
-
✅ Use
global
sparingly — overusing global variables can make debugging harder. -
✅ Use
nonlocal
in nested functions only when necessary. -
✅ Stick to function arguments and return values instead of relying on external state.
⚠️ Common Pitfalls
Pitfall | Why It’s Problematic |
---|---|
❌ Modifying a global variable without global |
Causes UnboundLocalError |
❌ Assuming nested functions always inherit variable values | Without nonlocal , changes inside don’t affect enclosing variables |
❌ Shadowing built-in names (like list , str ) |
Can lead to confusing bugs |
❌ Overuse of global scope | Reduces modularity and testability |
Summary Table
Scope | Description | Defined In |
---|---|---|
Local | Inside a function | Function body |
Enclosing | In a nested function’s parent | Outer function |
Global | Top-level script/module | Module |
Built-in | Python's built-in names | __builtins__ module |
Understanding Python's scoping rules empowers you to write cleaner, more reliable, and modular code. Mastering local
, global
, enclosing
, and built-in
scopes will save you from subtle bugs and boost your confidence in building complex applications.
Tips and Tricks
What is pass in Python?
Python | Pass Statement
The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.
def myfunction():
pass
How can you generate random numbers?
Python | Generate random numbers
Python provides a module called random using which we can generate random numbers. e.g: print(random.random())
We have to import a random module and call the random() method as shown below:
import random
print(random.random())
The random() method generates float values lying between 0 and 1 randomly.
To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
import random
print(random.randrange(5,100,2))
What is lambda in Python?
Python | Lambda function
A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
Syntex:
lambda arguments : expression
a = lambda x,y : x+y
print(a(5, 6))
It also provides a nice way to write closures. With that power, you can do things like this.
def adder(x):
return lambda y: x + y
add5 = adder(5)
add5(1) #6
As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
What is swapcase() function in the Python?
Python | swapcase() Function
It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
How to remove whitespaces from a string in Python?
Python | strip() Function | Remove whitespaces from a string
To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
What is the usage of enumerate() function in Python?
Python | enumerate() Function
The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
lst = ["A","B","C"]
print (list(enumerate(lst)))
#[(0, 'A'), (1, 'B'), (2, 'C')]
Can you explain the filter(), map(), and reduce() functions?
Python | filter(), map(), and reduce() Functions
- filter() function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
>>> set(filter(lambda x:x>4, range(7))) # {5, 6}
-
map() function calls the specified function for each item of an iterable and returns a list of result
>>> set(map(lambda x:x**3, range(7))) # {0, 1, 64, 8, 216, 27, 125}
-
reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:y-x, [1,2,3,4,5]) # 3
Let’s understand this:
2-1=1
3-1=2
4-2=2
5-2=3Hence, 3.
What is a namedtuple?
Python | namedtuple
A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.
>>> from collections import namedtuple
#format
>>> result=namedtuple('result','Physics Chemistry Maths')
#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80)
>>> Chris.Chemistry
# 92
Write a code to add the values of same keys in two different dictionaries and return a new dictionary.
We can use the Counter method from the collections module
from collections import Counter
dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}
new_dict = Counter(dict1) + Counter(dict2)
print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python In-place swapping of two numbers
Python | In-place swapping of two numbers
>>> a, b = 10, 20
>>> print(a, b)
10 20
>>> a, b = b, a
>>> print(a, b)
20 10
Reversing a String in Python
Python | Reversing a String
>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP
Python join all items of a list to convert into a single string
Python | Join all items of a list to convert into a single string
>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training
python return multiple values from functions
Python | Return multiple values from functions
>>> def A():
return 2, 3, 4
>>> a, b, c = A()
>>> print(a, b, c)
2 3 4
Python Print String N times
Python | Print String N times
>>> s = 'Python'
>>> n = 5
>>> print(s * n)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python | Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28