Lists#

Lists are the most versatile compound data type in Python. A list contains items separated by commas and enclosed within square brackets [ ].

Values are accessed using the slice operator [ ] and [ : ] with indexes starting at 0.

Built-in Functions#

Function	Description
`len(list)`	Total number of items in the list
`range(start, stop, step)`	Creates a sequence of numbers (returns an iterator in Python 3)
`sorted(list)`	Returns a new sorted list
`max(list)`	Returns the item with the maximum value
`min(list)`	Returns the item with the minimum value
`enumerate(list)`	Returns an iterator of (index, value) tuples
`set(list)`	Returns unique values from the list

List Methods#

Method	Description
`list.append(obj)`	Add an item to the end
`list.pop(index)`	Remove and return the item at position
`list.insert(index, obj)`	Insert object at the given position
`list.count(obj)`	Count occurrences of the object
`list.index(obj)`	Return the index of the first occurrence

Examples#

>>> a = ['spam', 'eggs', 100, 1234]
>>> a[3]
1234
>>> a[1:-1]
['eggs', 100]

>>> # Replace items
>>> a[0:2] = [1, 12]
>>> a
[1, 12, 100, 1234]

>>> # Remove items
>>> a[0:2] = []
>>> a
[100, 1234]

>>> # Insert items
>>> a[1:1] = ['bletch', 'xyzzy']
>>> a
[100, 'bletch', 'xyzzy', 1234]

>>> # Remove a specific item
>>> a.pop(a.index('xyzzy'))
'xyzzy'
>>> a
[100, 'bletch', 1234]

>>> b = [66.25, 333, -1, 333, 1, 1234.5]
>>> b.append(333)
>>> b
[66.25, 333, -1, 333, 1, 1234.5, 333]
>>> b.sort()
>>> b
[-1, 1, 66.25, 333, 333, 333, 1234.5]
>>> b.count(333)
3

>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> list(range(1, 11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> list(range(0, 30, 5))
[0, 5, 10, 15, 20, 25]

Note

In Python 3, range() returns an iterator, not a list. Wrap it with list() if you need an actual list.

Iteration#

>>> mylist = [33.2, 4674, "House"]
>>> for x in mylist:
...     print(x)
33.2
4674
House

>>> # Iterating two lists in parallel
>>> questions = ["name", "quest", "favorite color"]
>>> answers = ["lancelot", "the holy grail", "blue"]
>>> for q, a in zip(questions, answers):
...     print(q, a)
name lancelot
quest the holy grail
favorite color blue

>>> # Enumeration (index + value)
>>> mylist = ["tic", "tac", "toe"]
>>> for i, v in enumerate(mylist):
...     print(i, v)
0 tic
1 tac
2 toe

Filtering with fnmatch#

The fnmatch.filter() function filters a list using shell-style wildcards:

Pattern	Meaning
`*`	Matches everything
`?`	Matches any single character
`[seq]`	Matches any character in seq (`-` for range, `!` to exclude)

>>> import fnmatch
>>> lst = ['hor1', 'hor2', 'hor3', 'hor4', 'dff1', 'dff2', 'afr1']
>>> fnmatch.filter(lst, "a*")
['afr1']
>>> fnmatch.filter(lst, "dff?")
['dff1', 'dff2']
>>> fnmatch.filter(lst, "h*[1-3]")
['hor1', 'hor2', 'hor3']
>>> fnmatch.filter(lst, "[hd]*")
['hor1', 'hor2', 'hor3', 'hor4', 'dff1', 'dff2']
>>> fnmatch.filter(lst, "*[!1]")
['hor2', 'hor3', 'hor4', 'dff2']