--- title: Built-in Functions in Python source: https://app.sythra.ai/learn/python/built-in-functions-python topic: Python updated: 2026-08-12 publisher: Sythra (https://app.sythra.ai) --- # Built-in Functions in Python Built-in functions in Python are functions always available without any import, like type(), len(), range(), round(), max(), min(), and sum() — they cover type checking, numbers, and generating sequences. _Source: [https://app.sythra.ai/learn/python/built-in-functions-python](https://app.sythra.ai/learn/python/built-in-functions-python) — free to read on Sythra._ ## Key points - Built-in functions never need an import statement, unlike math or random - type() tells you the exact type; isinstance() asks a yes/no question about type - round() rounds to the nearest value; int() truncates instead - len() measures strings, lists, and other collections - range() generates a sequence that stops one before its end value Some tools are so commonly needed that Python does not make you import anything — they are always available the moment you start Python. These are called **built-in functions in Python**. Unlike [modules like math and random](/learn/python/libraries-and-modules-python), you never write an `import` line to use them. This page rounds up the built-ins you'll use constantly: checking and converting types, working with numbers, measuring things, and generating sequences. ## What you will learn - How `type()` and `isinstance()` differ - Converting between types with `int()`, `float()`, `str()` - Number built-ins: `abs()`, `round()`, `pow()`, `max()`, `min()`, `sum()` - Measuring things with `len()` - Generating sequences of numbers with `range()` ## Checking and converting types ```python type(42) # tells you what type something is type(3.14) # type('hello') # isinstance(42, int) # True is 42 an integer? yes isinstance(3.14, int) # False is 3.14 an integer? no isinstance('hello', str) # True is 'hello' a string? yes ``` `type()` tells you what kind of thing something is. `isinstance()` asks a yes-or-no question — _is this thing a particular type?_ — which makes it handy for guarding functions against bad input, as covered in [Recursion in Python](/learn/python/recursion-in-python). You can also convert between types (full details in [Type Casting in Python](/learn/python/type-casting)): ```python int(3.9) # 3 cuts off the decimal (does NOT round) float(5) # 5.0 turns a whole number into a decimal str(42) # '42' turns a number into text ``` These are useful when, for example, you want to join a number into a sentence — Python will not let you stick a number and a string together directly, but if you convert the number to a string first, it works fine. ## Numbers ```python abs(-7) # 7 the absolute value (removes the minus sign) round(3.7) # 4 rounds to nearest whole number round(3.14159, 2) # 3.14 rounds to 2 decimal places pow(2, 8) # 256 2 to the power of 8 max(3, 7, 2) # 7 the largest value min(3, 7, 2) # 2 the smallest value sum([1, 2, 3, 4]) # 10 adds everything in a list ``` `round()` is the one to reach for when you actually want rounding behavior — unlike `int()`, which always truncates toward zero regardless of how close a value is to the next whole number. ## Measuring things: len() ```python len('hello') # 5 how many characters in a string len([10, 20, 30]) # 3 how many items in a list ``` `len()` is one of the most used functions in Python — it works on strings, lists, and many other collection types. ## Generating sequences of numbers: range() ```python range(5) # 0, 1, 2, 3, 4 range(1, 6) # 1, 2, 3, 4, 5 range(0, 10, 2) # 0, 2, 4, 6, 8 (step of 2) ``` `range()` gives you a sequence of numbers. You will use this constantly in loops — for example, `for i in range(5)` repeats something five times. The sequence always stops _before_ the last number you give it — `range(5)` never includes `5` itself. > **Worth knowing:** ## Common mistakes - Comparing a boolean result with `== True` instead of using it directly - Expecting `int()` to round like `round()` does — it truncates instead - Assuming `range(5)` includes `5` — it stops one before the end value - Calling `len()` on something that has no length, like an integer, and hitting a `TypeError` - Confusing `type()`, which tells you the exact type, with `isinstance()`, which answers a yes/no question > **Practice with Sythra:** [Practice with AI tutor](https://app.sythra.ai/pricing) ## FAQ ### What are built-in functions in Python? Built-in functions are functions that are always available in Python without needing to import anything, such as type(), len(), range(), print(), max(), min(), and round(). ### What is the difference between type() and isinstance()? type() returns the exact type of a value, like . isinstance() answers a yes/no question about whether a value is a specific type, returning True or False, and is the preferred way to check types in conditionals. ### Does round() work the same as int() in Python? No. round() rounds to the nearest whole number (or a given number of decimal places), while int() truncates — it simply chops off the decimal part regardless of how close it is to rounding up. ### Does range(5) include the number 5? No. range(5) produces 0, 1, 2, 3, 4 — it always stops one before the value you give it as the end. ### What does len() do in Python? len() returns the number of items in a sequence, such as the number of characters in a string or the number of elements in a list. ## Related - [Functions in Python: Definition and How They Work](https://app.sythra.ai/learn/python/functions-in-python) — How def, parameters, and return values work. - [Libraries and Modules in Python](https://app.sythra.ai/learn/python/libraries-and-modules-python) — Functions that do need an import, like math and random. - [Type Casting in Python](https://app.sythra.ai/learn/python/type-casting) — The int(), float(), and str() conversion functions in depth. - [Python course hub](https://app.sythra.ai/learn/python) — All free Python explainers and the path into Agentic practice. - [Functions in Python in Depth: The Complete Guide](https://app.sythra.ai/learn/python/python-functions-in-depth) — Default args, *args/**kwargs, lambdas, and scope — all in one. --- Written by Sythra — Learn machine learning by building. 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