Quark’s Outlines: Python Built-in Functions

Overview, Historical Timeline, Problems & Solutions

An Overview of Python Built-in Functions

What is a Python built-in function?

You often need to do simple things in your code like find a number’s length or sort a list. Python gives you many built-in functions to help with these tasks. These functions work without importing any modules. They are always ready to use.

A Python built-in function is a name like len, print, or sum. It maps to a function written in the C language. These functions are part of the Python core. They run fast and follow strict rules for the number and types of values they accept.

Python lets you use fast, core functions like len() without imports.

name = "Ada"
print(len(name))  # prints: 3

The number of letters in the string is returned using len, a built-in function.

How are Python built-in functions different from user-defined ones?

You can make your own functions using the def keyword. Built-in functions are not made this way. They are written in C and added to Python when it runs. They are stored in a place called the built-in namespace.

Built-in functions often have special behavior that cannot be done in Python code. Some have limits on the kinds of values they can use. Each built-in function is a wrapper around a C function, not a Python function.

Python built-in functions are made in C, not with def.

print(callable(len))  # prints: True

The function len is callable, but not defined in Python code. It is built-in.

A Historical Timeline of Python Built-in Functions

Where do Python’s built-in functions come from?

Built-in functions are part of Python’s core. They reflect both programming needs and the language’s design values. Over time, Python added more of these functions, grouped them for clarity, and made their behavior consistent across data types.

People created core functions for math and strings

1989 — Python’s earliest sketches include ideas for functions like len, range, and print.

1991 — Python 0.9.0 released with early built-in functions: len, type, print, range, int, and str.

2000 — Python 2.0 introduced zip, filter, and map as built-in functions.

People cleaned up and grouped the built-ins

2008 — Python 3.0 removed apply, cmp, and others to make the built-in list shorter and more clear.

2010 — input replaced raw_input, and print became a proper function in Python 3.

2018 — The list of built-in functions was finalized to about 70 entries.

2024 — Python’s built-in functions are stable, fast, and documented in one place.

Problems & Solutions with Python Built-in Functions

How do you use Python built-in functions the right way?

Python gives you built-in functions to do everyday tasks like checking types, counting items, or changing data. These problems show how to use built-in functions instead of writing your own logic.

Problem: How do you find the length of a value in Python?

You are working with a list of names. You want to know how many names are in it. You do not want to use a loop or counter. You want the answer with a single command.

Problem: You want to count items in a list without writing your own loop.

Solution: Python lets you use the built-in function len() to return the number of items.

Python lets you count items with len().

names = ['Ada', 'Grace', 'Linus']
print(len(names))  # prints: 3

The len() function returns the count of items in the list.

Problem: How do you check if a value is a number in Python?

You are reading values from user input. You want to check if each value is an integer. You want to avoid crashes when users type the wrong thing.

Problem: You want to know if a value has a certain type.

Solution: Python lets you use the built-in function isinstance() to check types.

Python lets you test types with isinstance().

age = 30
print(isinstance(age, int))  # prints: True

This confirms that age is an integer before you do math with it.

Problem: How do you turn a string into a number in Python?

You have a string like "42" and you want to use it as a number. You do not want to write your own parser. You want a simple and safe way to convert it.

Problem: You want to convert text to a number.

Solution: Python lets you use int() or float() to turn strings into numbers.

Python lets you convert strings to numbers with int() and float().

text = "42"
print(int(text))  # prints: 42

The string is turned into a number you can use in math.

Problem: How do you get the largest value in a list in Python?

You are comparing numbers from a set of results. You want to know the highest score. You want a simple command to get it.

Problem: You need to find the largest number without writing a loop.

Solution: Python lets you use the max() function to return the biggest value.

Python lets you find the biggest value with max().

scores = [88, 95, 70, 100]
print(max(scores))  # prints: 100

The max() function returns the largest number in the list.

Problem: How do you run code when you don’t know the function name yet in Python?

You are writing a program that picks a function at runtime. The function name is stored in a variable. You want to call it without writing a long if-statement.

Problem: You want to call a function that is stored in a variable.

Solution: Python lets you call any callable object with (), including built-in functions.

Python lets you store and call functions like values.

f = len
print(f("Alan"))  # prints: 4

You can pass len around and use it like any other value.

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Mike Vincent is an American software engineer and app developer from Los Angeles, California. More about Mike Vincent