Common Mistakes with Built-in Functions in Python
Even though Python’s built-in functions are powerful, beginners often make small mistakes. Let’s explore common pitfalls and how to avoid them.
1) Using the Wrong Data Type
Many functions expect specific types of inputs. Passing incorrect types leads to errors.
# sum() expects an iterable of numbers
nums = [1, 2, 3]
print(sum(nums)) # 6
print(sum(5)) # TypeError
# int() conversion
print(int("123")) # 123
print(int("123.45")) # ValueError
2) Forgetting Parentheses
Functions must include parentheses to be called, otherwise Python returns the object itself.
print # <built-in function print>
print() # calls the function
# Common mistake with input
name = input # stores the function, not user input
name = input() # correct usage
3) Misusing Return Values
Some functions return values while others perform actions without returning. Understanding the return type is key.
nums = [5, 2, 9]
sorted(nums) # returns a new sorted list
print(nums) # original list unchanged
nums.sort() # sorts in-place, returns None
print(nums)
4) Mixing Function Names & Variables
sum = 10 # overrides built-in sum()
nums = [1,2,3]
print(sum(nums)) # TypeError, sum is now int
del sum # restores built-in sum
print(sum(nums)) # works fine
5) Common Logical Mistakes
- Confusing
isinstance()withtype()when checking inherited classes. - Using
any()andall()without understanding short-circuit behavior. - Expecting
input()to return a number without converting it first. - Overwriting built-in functions with variable names.
- Always check the documentation of a function using
help(). - Use meaningful variable names to avoid conflicts with built-ins.
- Understand expected input types and return values.
- Test functions with small examples before using in larger programs.
- Use
isinstance()to validate input types when needed.
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