List methods#
List is a mutable data type, so it is important to note that most list methods change a list in place without returning anything.
join#
Method join collects a list of strings into one string with separator
specified before join:
In [16]: vlans = ['10', '20', '30']
In [17]: ','.join(vlans)
Out[17]: '10,20,30'
Note
Method join actually string method but since the value must be
passed to it as a list, it is covered here.
append#
Method append adds specified item to the end of list:
In [18]: vlans = ['10', '20', '30', '100-200']
In [19]: vlans.append('300')
In [20]: vlans
Out[20]: ['10', '20', '30', '100-200', '300']
Method append changes list on spot and does not return anything.
extend#
If you want to combine two lists you can use one of two methods: extend
method or addition operation.
These methods have an important difference: extend changes list to
which method is applied and addition returns a new list that consists of two.
Method extend:
In [21]: vlans = ['10', '20', '30', '100-200']
In [22]: vlans2 = ['300', '400', '500']
In [23]: vlans.extend(vlans2)
In [24]: vlans
Out[24]: ['10', '20', '30', '100-200', '300', '400', '500']
Addition operation:
In [27]: vlans = ['10', '20', '30', '100-200']
In [28]: vlans2 = ['300', '400', '500']
In [29]: vlans + vlans2
Out[29]: ['10', '20', '30', '100-200', '300', '400', '500']
Note that when adding lists in IPython the ‘Out’ line appeared. This means that the result of summation can be assigned to variable:
In [30]: result = vlans + vlans2
In [31]: result
Out[31]: ['10', '20', '30', '100-200', '300', '400', '500']
pop#
Method pop removes item that corresponds to specified number. Method returns this item:
In [28]: vlans = ['10', '20', '30', '100-200']
In [29]: vlans.pop(-1)
Out[29]: '100-200'
In [30]: vlans
Out[30]: ['10', '20', '30']
Without number specified the last item in list is deleted.
remove#
Method remove removes specified item (remove does not return deleted item):
In [31]: vlans = ['10', '20', '30', '100-200']
In [32]: vlans.remove('20')
In [33]: vlans
Out[33]: ['10', '30', '100-200']
In remove you must specify item to be deleted, not its index. If item number is specified, error occurs:
In [34]: vlans.remove(-1)
-------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-32-f4ee38810cb7> in <module>()
----> 1 vlans.remove(-1)
ValueError: list.remove(x): x not in list
index#
Method index - returns the first index of the passed value:
In [35]: vlans = ['10', '20', '30', '100-200']
In [36]: vlans.index('30')
Out[36]: 2
insert#
Method insert allows to insert an item into a specific place in list:
In [37]: vlans = ['10', '20', '30', '100-200']
In [38]: vlans.insert(1, '15')
In [39]: vlans
Out[39]: ['10', '15', '20', '30', '100-200']
sort#
Method sort sorts list in place:
In [40]: vlans = [1, 50, 10, 15]
In [41]: vlans.sort()
In [42]: vlans
Out[42]: [1, 10, 15, 50]