list data structurein python . (continued..) .. [P-3]

[Humble]

Lists are one of the important data structure in python.

Lists are defined with the help of []

">>>> l=[]
>>> type(l)
<type 'list'>



lists can hold any data type in it..

>>>> l=[1, "how", 10.0]
>>> type(l)
<type 'list'>
>>>



lists are mutable !!!

That means you can change list entries/items..


Important functions ..




|  append(...)
|      L.append(object) -- append object to end
|  

>>>> l.append(100)
>>> l
[1, 'how', 10.0, 100]
>>> 

>>> j=[1,2,"second"]
>>> l.append(j)
>>> l
[1, 'how', 10.0, 100, [1, 2, 'second']]

>>> t= (1,3)
>>> type(t)
<type 'tuple'>
>>> l.append(t)
>>> l
[1, 'how', 10.0, 100, [1, 2, 'second'], (1, 3)]
>>> l[4]
[1, 2, 'second']
>>> l[5]
(1, 3)
>>> 




When you append **any ** item to end of list it goes as an 'entry'
in short 'append' take only one argument.. :)

|  count(...)
|      L.count(value) -> integer -- return number of occurrences of value
|  

>>>> l
[1, 'how', 10.0, 100, [1, 2, 'second'], (1, 3)]
>>> l.count(1)
1
>>> l.append(1)
>>> l
[1, 'how', 10.0, 100, [1, 2, 'second'], (1, 3), 1]
>>> l.count(1)
2




 |  extend(...)
|      L.extend(iterable) -- extend list by appending elements from the iterable

>>>> s="I am "
>>> l.extend(s)
>>> l
[1, 'how', 10.0, 100, [1, 2, 'second'], (1, 3), 1, 'I', ' ', 'a', 'm', ' ']
>>> 



 |
|  index(...)
|      L.index(value, [start, [stop]]) -> integer -- return first index of value.
|      Raises ValueError if the value is not present.

>>>> l.index("a")
9
>>> 
>>> l.index("l")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: 'l' is not in list
>>> 


 |
|  insert(...)
|      L.insert(index, object) -- insert object before index
|

>>>> l
[1, 'how', 10.0, 100, [1, 2, 'second'], (1, 3), 1, 'I', ' ', 'a', 'm', ' ']

>>> l.insert(2,20.0)
>>> l
[1, 'how', 20.0, 10.0, 100, [1, 2, 'second'], (1, 3), 1, 'I', ' ', 'a', 'm', ' ']
>>> 


"inserting" to an index is like a left push..


|  pop(...)
|      L.pop([index]) -> item -- remove and return item at index (default last).
|      Raises IndexError if list is empty or index is out of range.
|

To get /remove an item you can use 'pop':

>>>> l.pop(2)
20.0
>>> l
[1, 'how', 10.0, 100, [1, 2, 'second'], (1, 3), 1, 'I', ' ', 'a', 'm', ' ']
>>> 




|  remove(...)
|      L.remove(value) -- remove first occurrence of value.
|      Raises ValueError if the value is not present.

>>>> l.remove('how')
>>> l
[1, 10.0, 100, [1, 2, 'second'], (1, 3), 1, 'I', ' ', 'a', 'm', ' ']
>>> 




|
|  reverse(...)
|      L.reverse() -- reverse *IN PLACE*

>>>> l
[1, 10.0, 100, [1, 2, 'second'], (1, 3), 1, 'I', ' ', 'a', 'm', ' ']
>>> l.reverse()
>>> l
[' ', 'm', 'a', ' ', 'I', 1, (1, 3), [1, 2, 'second'], 100, 10.0, 1]
>>> 



To reverse a string I would do something like this :)

>>>> k="humble"
>>> z=[]
>>> z.extend(k)
>>> z
['h', 'u', 'm', 'b', 'l', 'e']
>>> z.reverse()
>>> z
['e', 'l', 'b', 'm', 'u', 'h']
>>> 


|
|  sort(...)
|      L.sort(cmp=None, key=None, reverse=False) -- stable sort *IN PLACE*;

>>>> for i in range(10):
...     l.append(random.randint(1,1000))
>>> l
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 850, 575, 910, 34, 436, 268, 218, 322, 212, 235]
>>> l.sort()
>>> l
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 34, 212, 218, 235, 268, 322, 436, 575, 850, 910]
>>> 





|      cmp(x, y) -> -1, 0, 1

>>>> l=[1,2]
>>> j=[3]
>>> cmp(l,j)
-1
>>> l
[1, 2]
>>> j
[1]
>>> j.append(2)
>>> cmp(l,j)
0
>>> 

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