Overwriting built-in functions

Python provides a rich set of built-in functions like sum(), max(), min(), list(), dict(), print(), and many more. These functions are essential for performing fundamental operations. However, accidentally overwriting built-in functions by assigning values to variables with the same names can lead to unexpected errors and debugging challenges.

Let’s explore this mistake step by step, understand why it happens, and how to avoid it.

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1. What Does It Mean to Overwrite a Built-in Function?

Overwriting a built-in function means assigning a value to a variable that has the same name as a built-in function, thereby replacing its original functionality in that scope.

Example of Overwriting a Built-in Function

sum = 10  # Overwrites the built-in sum() function

# Now trying to use sum() as a function will cause an error
numbers = [1, 2, 3, 4, 5]
print(sum(numbers))  # TypeError: 'int' object is not callable

Why is this a problem?

• The built-in sum() function is replaced by an integer (sum = 10).
• When sum(numbers) is called, Python treats sum as an integer instead of a function.
• This results in a TypeError because integers are not callable.

Fix: Use a different variable name.

total = 10  # Instead of sum
numbers = [1, 2, 3, 4, 5]
print(sum(numbers))  # Correct usage of built-in function

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2. Common Built-in Functions That Get Overwritten

Here are some commonly overwritten built-in functions:

Built-in Function	Accidental Overwriting Example
sum()	sum = 100
max()	max = 50
min()	min = 0
list()	list = [1, 2, 3]
dict()	dict = {"name": "Python"}
len()	len = 5
input()	input = "hello"
print()	print = "Hello World"
type()	type = "string"

These overwrites prevent the original function from being used until they are removed.

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3. How Overwriting Affects Code Execution

Example: Overwriting list()

list = [1, 2, 3, 4]  # Overwrites built-in list function

# Now trying to create a new list will cause an error
numbers = list((5, 6, 7))  
# TypeError: 'list' object is not callable

Fix: Use a different name.

my_list = [1, 2, 3, 4]  
numbers = list((5, 6, 7))  # Works fine

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Example: Overwriting print()

print = "Hello"  # Overwrites built-in print function

print("This will not work")  
# TypeError: 'str' object is not callable

Fix: Avoid naming variables as print.

message = "Hello"
print("This will work")  # Correct usage

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4. Detecting Overwritten Built-in Functions

If you suspect you’ve overwritten a built-in function, you can check its type using type().

Example

sum = 10  
print(type(sum))  # Output: <class 'int'>

Fix: Delete the variable to restore the built-in function.

del sum  # Deletes the overwritten variable
print(sum([1, 2, 3]))  # Works correctly now

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5. Best Practices to Avoid Overwriting Built-in Functions

1. Use Descriptive Variable Names total_sum = 10 # Instead of sum max_value = 100 # Instead of max
2. Check Before Assigning
   Before naming a variable, check if it conflicts with a built-in function: import builtins print("sum" in dir(builtins)) # True (exists in built-in functions)
3. Follow Naming Conventions
   • Use lowercase with underscores (snake_case).
   • Avoid using common function names.
4. Use IDE Warnings
   Many IDEs (like VS Code, PyCharm) will warn you when you overwrite a built-in function.

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6. Summary

Mistake	Issue	Fix
sum = 10	Overwrites sum()	Use total_sum = 10
list = [1, 2, 3]	Overwrites list()	Use my_list = [1, 2, 3]
print = "Hello"	Overwrites print()	Use message = "Hello"
max = 50	Overwrites max()	Use max_value = 50
dict = {"a": 1}	Overwrites dict()	Use my_dict = {"a": 1}