Python Built-in Functions Reference - 68 Python functions summarized

A Guide to Understanding Functions in Python

Beginner

Python Reference

This Python reference offers programmers a quick way to learn Python and also serves as a source for reminders.

While the version documented here is Python 3.5.3, most of this is suitable for other versions of Python 3, however check your version for details.

1. The Challenge

There are 3 types of functions in Python, built-in functions, those imported from other modules and user-defined functions.

The official Python.org website lists 68 built-in functions in one of the first reference documents in The Python Standard Library.

The challenge, for beginners especially, is understanding which functions to start with, so here we show you that list categorized and prioritized.

2. Python Built-In Functions

The table below lists 68 Python Built-in functions supplemented with Priority, Category and Description so you can develop a plan for what to memorize first and leave the rest to look up later.

Python Built-in Functions in Version 3.5.3
Function	Priority	Category	Description
`abs()`	High	Math	Absolute value of integer, float or complex number
`all()`	Mid	Logic	Returns True when all values are true.
`any()`	Mid	Logic	Returns True when any value is true.
`ascii()`	Mid	Strings	Return printable characters of an object with escaping.
`bin()`	Mid	Binary	Return a binary string for an integer.
`bool()`	Low	Boolean	Returns False if omitted or False values, otherwise True.
`bytearray()`	Low	Sequences	Return an array of bytes.
`bytes()`	Low	Bytes	Returns a new bytes type of object.
`callable()`	Mid	Logic	Returns True if object is callable, otherwise False.
`chr()`	High	Characters	Returns the character equivalent of the Unicode integer.
`classmethod()`	Low	Functions	Returns a class method for the supplied function.
`compile()`	Low	Compiling	Compiles source into code.
`complex()`	Low	Numbers	Returns a complex number from string or number.
`delattr()`	Low	Objects	Deletes an attribute from an object.
`dict()`	Mid	Dictionary	Create a new dictionary object.
`dir()`	Mid	Directory	Returns a list of names in the local scope, or attributes of the given object.
`divmod()`	Mid	Math	Returns the quotient and remainder for integers and floats.
`enumerate()`	Low	Objects	Returns an enumerate object.
`eval()`	Low	Code	Returns the result of an evaluated statement.
`exec()`	Low	Code	For dynamic execution of code.
`filter()`	Low	Functions	Construct an interator of values that return True
`float()`	High	Numbers	Returns a floating point number.
`format()`	Mid	Formatting	Returns input as formatted by a custom specification.
`frozenset()`	Mid	Containers	Returns a new frozenset object type.
`getattr()`	Mid	Attributes	Returns the value of the named attribute.
`globals()`	Mid	System	Returns a dictionary of names, methods and classes globally.
`hasattr()`	Mid	Attributes	Returns True if the object has a specified attribute.
`hash()`	Low	System	Returns hash integer keys for an object.
`help()`	High	Help	Invokes the built-in help system.
`hex()`	Mid	Numbers	Converts an integer to a lowercase hexadecimal string.
`id()`	Mid	Objects	Returns the unique id of an object.
`input()`	High	Interactivity	Reads a line from input as a string.
`int()`	High	Numbers	Returns an integer object constructed from a number or string.
`isinstance()`	Mid	Classes	Returns True if argument is an instance of a class.
`issubclass()`	Mid	Classes	Returns True if argument is an instance of a subclass
`iter()`	Mid	Loops	To iterate over an object like a set or tuple.
`len()`	High	Objects	Returns the length or number of items in an object.
`list()`	High	Lists	Create a mutable list object.
`locals()`	Mid	System	Returns a dictionary of names, methods and classes locally.
`map()`	Low	Iterables	Applies a function to each item of an iterable.
`max()`	High	Sorting	Returns the largest item from among iterables or arguments.
`memoryview()`	Low	Objects	Returns a memory view object from an argument.
`min()`	High	Sorting	Returns the smallest item from among iterables of arguments.
`next()`	Mid	Iterators	Returns the next item from an iterator.
`object()`	Mid	Objects	Returns a featureless object.
`oct()`	Mid	Numbers	Converts an integer into an octal string.
`open()`	High	Files	Open a file and create a file object.
`ord()`	Mid	Strings	Returns a Unicode integer for a string.
`pow()`	High	Math	Returns the exponent.
`print()`	High	Printing	Prints objects as text strings to the screen or standard output.
`property()`	Mid	Classes	Returns the property attribute for a class.
`range()`	High	Sequences	To create an immutable sequence type.
`repr()`	Mid	Strings	Returns object as a printable string
`reversed()`	Mid	Sequences	Returns a reverse interator.
`round()`	High	Numbers	Returns a number rounded to specified precision.
`set()`	Mid	Sets	Create a set object type.
`setattr()`	Mid	Attributes	Set's an attribute for a object.
`slice()`	Mid	Slice	Returns a slice object from another object.
`sorted()`	Mid	Lists	Return a sorted list object from an iterable object.
`staticmethod()`	Low	Classes	Returns a static method for a function.
`str()`	High	Strings	Returns the string version of an object.
`sum()`	High	Math	Returns the sum of an iterable object.
`super()`	Mid	Classes	To inherit methods from parent classes.
`tuple()`	High	Sequences	Create an immutable sequence type.
`type()`	High	Objects	Returns the type of object.
`vars()`	Mid	Objects	Returns the __dict__ attribute for objects that have them.
`zip()`	Low	Iterators	Creates an iterator of tuples.
`__import__()`	Mid	Modules	An internal Python function invoked during imports.

The Priority column was determined subjectively based on experience. Some have tried to scrape public Python code to rank functions and methods with limited success.

3. Find Built-in Functions For Your Version of Python

To find the built-in functions for your version, the easiest path is to go straight to the Python.org documentation page listing all versions.

After clicking the link to your version number, click Library Reference and then Built-in Functions.

4. Calling Functions in Python

For beginners, let's solidify how functions are called and introduce their syntax.

Let's create a text object, giving it a label x and use the most common function in Python called print() to print it to the screen.

>>> x = "I'm a string" >>> print(x) I'm a string

We put the label (often called a variable) inside the function's parentheses thereby telling Python what to print. Here we are calling the function and sending it an argument.

What we didn't note here is that the print() function can take optional arguments, or multiple arguments, as you can see here.

>>> print(x, x) I'm a string I'm a string # note the space between the two strings >>> print() # no errors, a blank line printed

In the first case we gave the function two arguments and in the second we gave it none.

Now you wouldn't know what arguments to send to a function without knowing the syntax for each function. So next we'll see how to look that up.

5. Accessing Python Function Syntax on your Local Machine

You can find the syntax for functions at the Python.org website as mentioned earlier, or you may find it less distracting and faster to use local help right in the Python Interpreter.

Entering help('print') at the Python Interpreter will show syntax for the print function, like this.

Help on built-in function print in module builtins: print(...) print(value, ..., sep=' ', end='\n, file=sys.stdout, flush=False) Prints the values to a stream, or to sys.stdout by default. Optional keyword arguments: file: a file-like object (stream); defaults to the current sys.stdout. sep: string inserted between values, default a space. end: string appended after the last value, default a newline. flush: whether to forcibly flush the stream. (END)

We won't cover all of it, but in a nutshell the sytax shows that multiple arguments can be entered and the optional keyword arguments sep=' ' explains why there was a space between the strings earlier. The end='\n' demonstrates why there was a blank line when we didn't enter any arguments. These were the defaults, and they could be overridden by specifying these arguments.

This is one short example that demonstrates function syntax and shows how you can save time by looking for function syntax right at the Python Interpreter.

Python Reference: 68 Python Built-In Functions Summarized