Overview
List is one of the simplest and most important data structures in Python.
Lists are enclosed in square brackets [ ] and each item is separated by a comma.
Lists are collections of items where each item in the list has an assigned index value.
A list is mutable, meaning you can change its contents.
Lists are very fexible and have many built-in control functions.
- Built-in List Methods in Python
- Python Programming – Python Lists
- Python Programming – List Functions And Methods
Methods of List objects
Calls to list methods have the list they operate on appear before the method name separated by a dot, e.g. L.reverse()
Creation
L = ['yellow', 'red', 'blue', 'green', 'black']
>>>print L
returns: ['yellow', 'red', 'blue', 'green', 'black']
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Accessing / Indexing
L[0] = returns 'yellow'
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Slicing
L[1:4] = returns ['red', 'blue', 'green']
L[2:] = returns ['blue', 'green', 'black']
L[:2] = returns ['yellow', 'red']
L[-1] = returns 'black'
L[1:-1] = returns ['red', 'blue', 'green']
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Length - number of items in list
len(L) = returns 5
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Sorting - sorting the list
sorted(L) = returns ['black', 'blue', 'green', 'red', 'yellow']
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Append - append to end of list
L.append("pink")
>>> print L
returns: ['black', 'blue', 'green', 'red', 'yellow', 'pink']
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Insert - insert into list
L.insert(0, "white")
>>> print L
returns: ['white', 'black', 'blue', 'green', 'red', 'yellow', 'pink']
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Extend - grow list
L.extend(L2)
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Remove - remove first item in list with value "white"
L.remove("white")
>>> print L
returns: ['black', 'blue', 'green', 'red', 'yellow', 'pink']
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Delete
Remove an item from a list given its index instead of its value
del.L[0]
>>> print L
['blue', 'green', 'red', 'yellow', 'pink']
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Pop
Remove last item in the list
L.pop() = returns 'pink'
# remove indexed value from list
L.pop(1) = returns 'green'
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Reverse - reversing the list
L.reverse()
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Count
Search list and return number of instances found
L.count('red')
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Keyword "in" - can be used to test if an item is in a list
if 'red' in L:
print "list contains", 'red'
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For-in statement - makes it easy to loop over the items in a list
for item in L:
print item
L = ['red', 'blue', 'green']
for col in L:
print col