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Python Reference: 68 Python built-in functions summarized

Don't let the list intimidate you. Here's a plan to break the problem into digestible chunks.
  1. The Challenge - Acknowledge why it's easy to feel inundated.
  2. The List - See built-ins prioritized, categorized and summarized.
  3. Versions - Find the list for your Python version.
  4. Calling - Describe how functions are called.
  5. Syntax - Access docs for built-in function locally.
Paul Alan Davis, CFA, November 30, 2018
Updated: December 3, 2018
This page offers a way to explore native Python functions and then take that understanding to learn how to use other functions, or write your own. Keep reading.

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A Guide to Understanding Functions in Python


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.

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