Quick Jump List
A:
abs,
aiter,
all,
anext,
any,
ascii,
B:
bin,
bool,
breakpoint,
bytearray,
bytes,
C:
callable,
chr,
classmethod,
compile,
complex,
D:
delattr,
dict,
dir,
divmod
E:
enumerate,
eval,
exec,
F:
filter,
float,
format,
frozenset,
G:
getattr,
globals,
H:
hasattr,
hash,
help,
hex,
I:
id,
input,
int,
isinstance,
issubclass,
iter,
L:
len,
list,
locals,
M:
map,
max,
memoryview,
min,
N:
next,
O:
object,
oct,
open,
ord,
P:
pow,
print,
property,
R:
range,
repr,
reversed,
round,
S:
set,
setattr,
slice,
sorted,
staticmethod,
str,
sum,
super,
T:
tuple,
type,
V:
vars,
Z:
zip,
_:
__import__,
Motivation
The Python docs are ill-suited to novices.
The content of the built-in functions documentation favors precision and correctness over comprehension for beginners. While this style is great for experienced developers who already understand the finer points of Python’s design, the docs are confusing to novice programmers like a 12 year old who is not far on his journey of learning Python.
This guide is an opinionated and simplified description of Python’s built-in functions.
My goal is to provide definitions, in plain English, of each built-in function that comes with Python. Along with each definition is an example that is as simple as I can think of. I ran each example against the latest version of Python as of the time writing this guide.
I want to be able to share this with my 12 year old son or my 10 year old daughter, so that they can understand and use Python. My hope is that this guide also serves others who would like some plain definitions of what the built-in functions do.
A note for pedants: I am sacrificing precision and exactness in favor of comprehension. That means I will use substitionary language that I think will communicate more clearly than the exact terminology. If you’re looking for that level of precision, please refer to the standard library docs. Those docs are great for that level of clarity.
For the rest of us, let’s go!
abs
abs returns the absolute value of a number, which means it
removes any negative sign. The result is always a positive number or zero.
Example:
>>> abs(-5)
5
>>> abs(3.2)
3.2
aiter
aiter is the asynchronous version of iter.
This allows you to iterate over asynchronous data sources, such as
streams, one item at a time in an asynchronous loop.
If this example looks intimidating, fear not! Asynchronous programming is a more advanced Python concept. You are unlikely to encounter this much in a lot of Python code.
Example:
>>> import asyncio
>>> from collections.abc import AsyncIterable
>>> class AsyncRange(AsyncIterable):
... def __init__(self, start, end):
... self.start = start
... self.end = end
... async def __aiter__(self):
... for i in range(self.start, self.end):
... await asyncio.sleep(0.1)
... yield i
...
>>> async def example():
... async for i in aiter(AsyncRange(1, 4)):
... print(i)
...
>>> asyncio.run(example())
1
2
3
all
all returns True if all elements in something list-like (such as a
list or tuple) are “truthy” or if the list is empty.
If any element is false, it returns False.
Example:
>>> all([True, True, True])
True
>>> all([True, False, True])
False
>>> all([1, 2, 3])
True
>>> all([])
True
anext
anext is the asynchronous version of next.
If the iterator is exhausted, it can raise a StopAsyncIteration
exception unless a default value is provided.
If this example looks intimidating, fear not! Asynchronous programming is a more advanced Python concept. You are unlikely to encounter this much in a lot of Python code.
Example:
>>> import asyncio
>>> from collections.abc import AsyncIterable
>>> class AsyncRange(AsyncIterable):
... def __init__(self, start, end):
... self.start = start
... self.end = end
... async def __aiter__(self):
... for i in range(self.start, self.end):
... await asyncio.sleep(0.1)
... yield i
...
>>> async def example():
... it = aiter(AsyncRange(1, 4))
... print(await anext(it))
... print(await anext(it))
...
>>> asyncio.run(example())
1
2
any
any returns True if at least one element in something list-like
(such as a list or tuple) is true. If all elements are false or if the
list is empty, it returns False.
Example:
>>> any([False, False, False])
False
>>> any([False, False, True])
True
>>> any([])
False
ascii
ascii returns a string containing a printable representation
of an object. It escapes non-ASCII characters in the string using Unicode
escape sequences, so the result can be safely printed or used where only
ASCII characters are allowed.
Example:
>>> ascii('Hello, world!')
"'Hello, world!'"
>>> ascii('Héllo')
"'H\\xe9llo'"
bin
bin converts an integer number to a binary string prefixed
with 0b. The result is a string that represents the binary equivalent of
the number.
Example:
>>> bin(10)
'0b1010'
>>> bin(255)
'0b11111111'
bool
bool converts a value to a Boolean (True or False).
If the value is considered true (e.g., non-zero numbers, non-empty lists),
it returns True. Otherwise, it returns False.
Example:
>>> bool(0)
False
>>> bool(1)
True
>>> bool([])
False
>>> bool([1, 2, 3])
True
breakpoint
breakpoint is used to pause the execution of a program and
start an interactive debugger at that point. It is helpful for inspecting
the state of a program during debugging.
Example:
>>> def example():
... x = 10
... breakpoint()
... print(x)
...
>>> example()
> <stdin>(4)example()
(Pdb) x
10
(Pdb) c
10
bytearray
bytearray creates a modifiable sequence of bytes. It can be set
with a string, a sequence of integers, or an iterable of bytes, and allows
modification of the byte values.
Example:
>>> ba = bytearray('hello', 'utf-8')
>>> ba
bytearray(b'hello')
>>> ba[0] = 72
>>> ba
bytearray(b'Hello')
bytes
bytes creates an unmodifiable sequence of bytes. It can be initialized
with a string, a sequence of integers, or an iterable of bytes.
Unlike bytearray, the result cannot be modified after creation.
Example:
>>> b = bytes('hello', 'utf-8')
>>> b
b'hello'
>>> b[0] = 72
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'bytes' object does not support item assignment
>>> b = bytes([65, 66, 67])
>>> b
b'ABC'
callable
callable checks if an object appears to be callable, meaning it can
be called like a function. It returns True if the object can be called, and
False otherwise.
Example:
>>> callable(print)
True
>>> callable(42)
False
chr
chr converts an integer (representing a Unicode code point) to
its corresponding character. It returns the character as a string.
It is the inverse of ord.
Example:
>>> chr(65)
'A'
>>> chr(128513)
'😁'
classmethod
classmethod is used to define a method in a class that is connected
to the class.
This means that the method receives the class as its first argument
instead of an instance.
Example:
>>> class Example:
... @classmethod
... def greet(cls):
... return f"Hello from {cls.__name__}"
...
>>> Example.greet()
'Hello from Example'
compile
compile builds source code into a code object that can be executed
by the exec() or eval() functions. It takes a string of code and returns a
code object which can be run later.
Example:
>>> code = compile('print("Hello, world!")', '<string>', 'eval')
>>> exec(code)
Hello, world!
complex
complex creates a complex number from a real and an optional imaginary
part. The result is a number with both real and imaginary components.
In math, you would typically use i to represent the imaginary portion.
Because i is a common variable name, Python uses j instead.
Example:
>>> complex(2, 3)
(2+3j)
>>> complex('1+2j')
(1+2j)
delattr
delattr removes an attribute from an object. You need to provide
the object and the name of the attribute as a string. If the attribute does not
exist, it raises an AttributeError.
Example:
>>> class Example:
... def __init__(self):
... self.an_attribute = 10
...
>>> example = Example()
>>> delattr(example, 'an_attribute')
>>> example.an_attribute
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'Example' object has no attribute 'an_attribute'
dict
dict creates a dictionary, which is a collection of key-value pairs.
You can initialize it with key-value pairs, or with other mappings or sequences.
More commonly, dictionaries will be constructed from the literal syntax
using { and }.
Example:
>>> d = dict(a=1, b=2)
>>> d
{'a': 1, 'b': 2}
>>> d = dict([('a', 1), ('b', 2)])
>>> d
{'a': 1, 'b': 2}
>>> d = {'a': 1, 'b': 2}
>>> d
{'a': 1, 'b': 2}
dir
dir returns a list of valid attributes for an object.
If no object is passed, it returns a list of names in the current local scope.
Example:
>>> class MyClass:
... def method(self):
... pass
...
>>> dir(MyClass)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__',
'__format__', '__ge__', '__getattribute__', '__gt__', '__hash__',
'__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__',
'__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__',
'__str__', '__subclasshook__', 'method']
>>> dir()
['__builtins__', '__cached__', '__doc__', '__import__', '__loader__',
'__name__', '__package__', '__spec__', '__stderr__', '__stdin__',
'__stdout__']
divmod
divmod takes two numbers and returns a tuple containing their quotient
and remainder.
This is like division before you learned fractions in math class.
In my math memory, I would write something like “9 / 4 = 2r1”.
The “2” and the remainder of “1” are what divmod returns.
Example:
>>> divmod(9, 4)
(2, 1)
>>> divmod(15, 6)
(2, 3)
enumerate
enumerate gives a counting number along with values when looping on something list-like.
You can change where the counting number starts by using the start keyword argument.
Example:
>>> for index, value in enumerate(['apple', 'banana']):
... print(index, value)
...
0 apple
1 banana
>>> for index, value in enumerate(['cherry', 'date'], start=1):
... print(index, value)
...
1 cherry
2 date
eval
eval evaluates a string containing Python code and returns the result.
Be careful when using eval with untrusted data, as it can execute arbitrary code.
Example:
>>> eval('2 + 3')
5
>>> x = 10
>>> eval('x * 2')
20
exec
exec executes a string containing Python code. Unlike eval, which only evaluates
expressions (i.e., simple code that returns a value),
exec can execute complex code including statements, functions, and class definitions.
Be careful when using exec with untrusted data, as it can execute arbitrary code.
Example:
>>> code = '''
... def greet(name):
... return f"Hello, {name}!"
... '''
>>> exec(code)
>>> greet('Alice')
'Hello, Alice!'
filter
filter takes something list-like and checks every value with a function
that returns either True or False.
Only the values that return True are included in the result.
When the function is None, the resulting list only includes items that are truthy.
Example:
>>> def is_even(n):
... return n % 2 == 0
...
>>> list(filter(is_even, [1, 2, 3, 4]))
[2, 4]
>>> list(filter(None, [0, 1, 2, '', 'hello']))
[1, 2, 'hello']
float
float converts a number or a string to a floating-point number. It can handle
integer values, floating-point literals, and strings representing numbers.
Example:
>>> float(10)
10.0
>>> float('3.14')
3.14
>>> float('1e-4')
0.0001
format
format outputs a value according to a specified format string. It allows you
to control how numbers and strings are presented, such as setting decimal places or padding.
There are lots of options you can learn about to do string formatting. All the messy details are in the Format Specification.
Example:
>>> format(123.4567, '.2f')
'123.46'
>>> format(42, '04d')
'0042'
>>> format('hello', '^10')
' hello '
frozenset
frozenset creates an unmodifiable version of a set.
It can be set with anything list-like, and supports set operations
like unions and intersections, but without the ability to add or remove elements.
Example:
>>> fs = frozenset([1, 2, 3, 4])
>>> fs
frozenset({1, 2, 3, 4})
>>> fs2 = frozenset([3, 4, 5, 6])
>>> fs | fs2 # Union
frozenset({1, 2, 3, 4, 5, 6})
>>> fs & fs2 # Intersection
frozenset({3, 4})
getattr
getattr retrieves the value of an attribute from an object. If the attribute does
not exist, it can return a default value if provided; otherwise, it raises an AttributeError.
Example:
>>> class Example:
... def __init__(self):
... self.an_attribute = 10
...
>>> example = Example()
>>> getattr(example, 'an_attribute')
10
>>> getattr(example, 'another_attribute', 42)
42
globals
globals returns a dictionary representing the current global symbol table.
This dictionary contains all the global variables and their values in the current scope.
Example:
>>> x = 10
>>> globals()
{'__name__': '__main__', '__doc__': None,
'__import__': <built-in function __import__>, 'x': 10, ...}
>>> globals()['x']
10
hasattr
hasattr checks if an object has a specified attribute. It returns True
if the attribute exists and False otherwise.
Example:
>>> class Example:
... def __init__(self):
... self.an_attribute = 10
...
>>> example = Example()
>>> hasattr(example, 'an_attribute')
True
>>> hasattr(example, 'another_attribute')
False
hash
hash returns the hash value of an object, which is an integer used for
hash-based operations like dictionary key lookups. The object must be immutable
(i.e., unchanging), such as strings, numbers, or tuples containing only immutable elements.
Example:
>>> hash('hello')
-9108665849909559950
>>> hash((1, 2, 3))
529344067295497451
help
help provides a helpful summary of information about an object,
such as a module, function, class, or method.
It displays documentation and usage information.
Example:
>>> help(abs)
Help on built-in function abs in module builtins:
abs(x, /)
Return the absolute value of the argument.
hex
hex converts an integer to a hexadecimal string, prefixed with 0x.
The result represents the number in base-16 notation.
Example:
>>> hex(255)
'0xff'
>>> hex(1234)
'0x4d2'
id
id returns a unique identifier for an object. This identifier is a constant integer
that is guaranteed to be unique and constant for the object during its lifetime.
Example:
>>> x = 'hello'
>>> id(x)
4512339488
>>> y = [1, 2, 3]
>>> id(y)
4513728448
input
input reads a line of text from the user and returns it as a string.
You can provide a prompt string that is displayed to the user before they enter their input.
Example:
>>> name = input('Enter your name: ')
Enter your name: Bob
>>> name
'Bob'
int
int converts a number or a string to an integer. It can handle decimal
numbers and strings representing integers, as well as numbers in other bases if specified.
Example:
>>> int('42')
42
>>> int(3.14)
3
>>> int('101', base=2) # Convert binary string to integer
5
isinstance
isinstance checks if an object is an instance or subclass of a specified class
or tuple of classes. It returns True if the object matches the class, and False otherwise.
Example:
>>> isinstance(10, int)
True
>>> isinstance('hello', int)
False
>>> isinstance('hello', str)
True
>>> isinstance(10, (float, int))
True
>>> isinstance([], list)
True
issubclass
issubclass checks if a class is a subclass of another class or a tuple of classes.
It returns True if the class is a subclass, and False otherwise.
Example:
>>> class A:
... pass
...
>>> class B(A):
... pass
...
>>> issubclass(B, A)
True
>>> issubclass(A, B)
False
>>> issubclass(B, (A, object))
True
iter
iter returns an iterator object for something list-like.
Iterators allow you to traverse through items one at a time.
Example:
>>> it = iter([1, 2])
>>> next(it)
1
>>> next(it)
2
>>> next(it)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
len
len (for “length”) returns the number of items in something list-like, such as a list, tuple,
or string. It provides the count of elements or characters contained in the object.
Example:
>>> len([1, 2, 3])
3
>>> len((1, 2, 3, 4))
4
>>> len('hello')
5
list
list creates a new list object from an iterable or sequence. If no argument is
provided, it returns an empty list. It is commonly used to convert other data types into lists.
More commonly, lists are constructed from the literal syntax
using [ and ].
Example:
>>> list('abc')
['a', 'b', 'c']
>>> list((1, 2, 3))
[1, 2, 3]
>>> list(range(3))
[0, 1, 2]
>>> [1, 2]
[1, 2]
locals
locals returns a dictionary representing the current local symbol table.
This dictionary includes all local variables and their values in the current scope.
Example:
>>> def example():
... x = 10
... y = 20
... return locals()
...
>>> example()
{'x': 10, 'y': 20}
map
map applies a specified function to each item in something list-like
and returns the results. It is useful for processing or transforming
elements in a collection.
Example:
>>> def square(x):
... return x * x
...
>>> list(map(square, [1, 2, 3, 4]))
[1, 4, 9, 16]
>>> list(map(str, [1, 2, 3]))
['1', '2', '3']
max
max returns the largest item from something list-like or among two or more arguments.
It can also take a key function to determine the maximum value based on custom criteria.
Example:
>>> max([1, 2, 3, 4])
4
>>> max(10, 20, 30)
30
>>> max(['apple', 'banana', 'pear'], key=len)
'banana'
memoryview
memoryview creates a memory view object from a bytes-like object.
This view allows you to access the data without copying it.
It is useful for handling large data buffers more efficiently.
Example:
>>> mv = memoryview(b'hello')
>>> mv[0]
104
>>> mv[1:4].tobytes()
b'ell'
min
min returns the smallest item from something list-like or among two or more arguments.
It can also take a key function to determine the minimum value based on custom criteria.
Example:
>>> min([1, 2, 3, 4])
1
>>> min(10, 20, 30)
10
>>> min(['apple', 'banana', 'pear'], key=len)
'pear'
next
next retrieves the next item from an iterator. You can also provide a default value
to return if the iterator is exhausted; otherwise, it raises a StopIteration exception.
Example:
>>> it = iter([1, 2])
>>> next(it)
1
>>> next(it)
2
>>> next(it, 'No more items')
'No more items'
>>> next(it)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
object
object returns a new featureless object.
This is the base for all objects in Python.
Example:
>>> obj = object()
>>> obj
<object object at 0x10bb88a60>
>>> isinstance(obj, object)
True
oct
oct converts an integer to its octal string representation, prefixed with 0o.
This string represents the number in base-8 notation.
Example:
>>> oct(8)
'0o10'
>>> oct(64)
'0o100'
open
open opens a file and returns a file object. You can specify the mode in which
the file is opened (e.g., read, write).
Example:
>>> with open('example.txt', 'w') as f:
... f.write('Hello World')
...
11
>>> with open('example.txt') as f:
... content = f.read()
...
>>> content
'Hello World'
ord
ord function returns the Unicode code point of a single character string.
This integer represents the character in Unicode.
It is the inverse of chr.
Example:
>>> ord('A')
65
>>> ord('😁')
128513
pow
pow calculates the power of a number.
This function behaves like the ** operator (e.g., 2**3).
Example:
>>> pow(2, 3)
8
print outputs text or other data to the console. You can provide multiple arguments,
and it will convert them to strings and display them, separated by spaces. You can also specify end
characters and separators.
Example:
>>> print('Hello, world!')
Hello, world!
>>> print('The answer is', 42)
The answer is 42
>>> print('Hello', end='!\n')
Hello!
property
property creates a property attribute in a class. This allows you to define methods
that can be accessed like attributes. You can use it to control access to attributes and define custom
getter, setter, and deleter methods.
Example:
>>> class Example:
... def __init__(self, value):
... self._value = value
... @property
... def value(self):
... return self._value
... @value.setter
... def value(self, new_value):
... self._value = new_value
...
>>> example = Example(10)
>>> example.value
10
>>> example.value = 20
>>> example.value
20
range
range generates counting numbers, starting from a specified start value up to,
but not including, an end value. It can also accept a step value to define the increment between numbers.
Example:
>>> list(range(5))
[0, 1, 2, 3, 4]
>>> list(range(2, 8))
[2, 3, 4, 5, 6, 7]
>>> list(range(1, 10, 2))
[1, 3, 5, 7, 9]
repr
repr returns a string that represents an object in a way that could be used to recreate
the object, if possible. It is intended for debugging and development, and often includes more details
than the string representation provided by str.
Example:
>>> repr('hello')
"'hello'"
>>> repr([1, 2, 3])
'[1, 2, 3]'
>>> repr({'key': 'value'})
"{'key': 'value'}"
reversed
reversed returns something list-like in the reverse order.
It does not modify the original.
Example:
>>> list(reversed([1, 2, 3, 4]))
[4, 3, 2, 1]
>>> list(reversed('hello'))
['o', 'l', 'l', 'e', 'h']
round
round takes a number and rounds to a specified number of decimal places.
If no number of decimal places is specified, it rounds to the nearest whole number.
Example:
>>> round(3.14159, 2)
3.14
>>> round(2.71828)
3
>>> round(1.5)
2
set
set creates a new set from something list-like.
Sets are collections of unique elements and support operations like unions, intersections, and differences.
Sets are commonly constructed from the literal syntax
using { and }.
Example:
>>> set([1, 2, 3, 2, 1])
{1, 2, 3}
>>> set('hello')
{'h', 'e', 'l', 'o'}
>>> set()
set()
>>> type({1, 2, 3, 4})
<class 'set'>
setattr
setattr sets the value of an attribute on an object.
If the attribute does not already exist, it is created.
You provide the object, the name of the attribute, and the value to set.
Example:
>>> class Example:
... def __init__(self):
... self.an_attribute = 10
...
>>> example = Example()
>>> example.an_attribute
10
>>> setattr(example, 'an_attribute', 20)
>>> example.an_attribute
20
>>> setattr(example, 'another_attribute', 30)
>>> example.another_attribute
30
slice
slice creates a slice object that specifies how to extract part of something list-like.
It takes up to three arguments: start, stop, and step.
More commonly, slices use the literal syntax of : for conciseness (e.g., items[1:4]).
Example:
>>> s = slice(1, 4)
>>> items = [10, 20, 30, 40, 50]
>>> items[s]
[20, 30, 40]
>>> s = slice(0, 4, 2)
>>> items[s]
[10, 30]
>>> items[1:4]
[20, 30, 40]
sorted
sorted returns a new list containing all items from something list-like,
sorted in ascending order.
You can also provide a custom sorting function
and specify whether to sort in ascending or descending order.
Example:
>>> sorted([3, 1, 4, 1, 5, 9])
[1, 1, 3, 4, 5, 9]
>>> sorted(['apple', 'banana', 'pear'], key=len)
['pear', 'apple', 'banana']
>>> sorted([3, 1, 4, 1, 5, 9], reverse=True)
[9, 5, 4, 3, 1, 1]
staticmethod
staticmethod defines a method within a class
that does not depend on class or instance-specific data.
Example:
>>> class Example:
... @staticmethod
... def greet(name):
... return f'Hello, {name}!'
...
>>> Example.greet('Mark')
'Hello, Mark!'
str
str converts an object to its string representation. This is useful for displaying
or working with textual data. You can use it to convert numbers, lists, or other objects into strings.
Example:
>>> str(123)
'123'
>>> str(3.14)
'3.14'
>>> str([1, 2, 3])
'[1, 2, 3]'
sum
sum adds up all the items in something list-like containing numbers.
Example:
>>> sum([1, 2, 3, 4])
10
>>> sum((10, 20, 30))
60
>>> sum(range(5))
10
super
super returns a proxy object that represents the parent classes of the current class.
It is used to call methods from a parent class, allowing you to extend or modify inherited methods.
Example:
>>> class A:
... def greet(self):
... return 'Hello from A'
...
>>> class B(A):
... def greet(self):
... return super().greet() + ' and B'
...
>>> b = B()
>>> b.greet()
'Hello from A and B'
tuple
tuple creates a new tuple object from something list-like.
Tuples are immutable, meaning their contents cannot be changed after creation.
If no argument is provided, it returns an empty tuple.
Example:
>>> tuple([1, 2, 3])
(1, 2, 3)
>>> tuple('abc')
('a', 'b', 'c')
>>> tuple()
()
type
type function returns the type of an object, which is a class that the object belongs to.
Example:
>>> type(123)
<class 'int'>
>>> type('hello')
<class 'str'>
>>> type([1, 2, 3])
<class 'list'>
>>> class Example:
... pass
...
>>> type(Example())
<class '__main__.Example'>
vars
vars returns the __dict__ attribute of an object, which is a dictionary containing
its writable attributes.
If no object is provided, it returns the __dict__ of the current local symbol table.
Example:
>>> class Example:
... def __init__(self):
... self.an_attribute = 'value1'
... self.another_attribute = 'value2'
...
>>> example = Example()
>>> vars(example)
{'an_attribute': 'value1', 'another_attribute': 'value2'}
>>> vars()
{'__name__': '__main__', '__doc__': None, '__package__': None, ...}
zip
zip takes two or more list-like things and aggregates their items into tuples.
Each tuple contains elements from the corresponding positions of the inputs. If the
inputs are of different lengths, zip stops at the shortest one.
Example:
>>> list(zip([1, 2, 3], ['a', 'b', 'c']))
[(1, 'a'), (2, 'b'), (3, 'c')]
>>> list(zip('abc', [1, 2, 3], [True, False, True]))
[('a', 1, True), ('b', 2, False), ('c', 3, True)]
>>> list(zip([1, 2], ['x', 'y', 'z']))
[(1, 'x'), (2, 'y')]
__import__
__import__ is a low-level function used by the import statement to load modules.
It takes a module name as a string and returns the imported module.
You should probably use import instead.
Example:
>>> math = __import__('math')
>>> math.sqrt(16)
4.0
>>> os = __import__('os')
>>> os.name
'posix'
