Sorting Python List To Make Letters Come Before Numbers

I'm pretty new to python and I'm looking for a way to sort a list placing words before numbers. I understand you can use sort to do the following : a = ['c', 'b', 'd', 'a'] a.sort(

Solution 1:

You could provide a custom key argument which gives a lower value to strings than it does to ints:

>>> c = ['c', 'b', 'd', 'a', 4, 2, 1, 3]
>>> c.sort(key = lambda item: ([str,int].index(type(item)), item))
>>> c
['a', 'b', 'c', 'd', 1, 2, 3, 4]

Solution 2:

[sorted([letter for letter in c ifisinstance(letter, str)]) + \
 sorted([number for number in c ifisinstance(number, int)]]

Should do it.

Solution 3:

Let's say we have a hybrid list like this:

c = ['s', 'a',2 , 'j', 9, 'e', 11, 't', 'k', 12, 'q']

first we need to slice up the list into two separate parts (strings and integers), sort them individually and then append them in the end. Here's one way to do it:

>>>c = sorted([i for i in c ifnotstr(i).isdigit()]) + sorted([i for i in c ifstr(i).isdigit()])

Now you get:

>>> c
['a', 'e', 'j', 'k', 'q', 's', 't', 2, 9, 11, 12]

Solution 4:

If you have a list of mixed ascii and numeric types, you need to determine what is a numeric object type. You can use the Numbers abstract base class to determine what is an instance of a number (int, float, long, complex) class, including all derived classes (bool, Decimal, Franctions, etc):

>>> from numbers import Number
>>> [isinstance(n, Number) for n in (0,1.1,0j,True,'a')]
[True, True, True, True, False]

Once you know what is an instance of a number, you can use a Python bool to create a primary sort key with the list item itself as a secondary key (ie, tuples comprising of [(True, 1.1), (False, 'abc'), etc]) False will sort lower than True just as 0<1 in a typical ascending order sort, so that is just what we wanted.

Applying that to your list (expanded) as an example:

>>> c = ['c', 'b', 'd', 'a', 4, 2, 1, 35, 1.1, 6L, 'aac', True]
>>> sorted(c, key=lambda e: (isinstance(e, Number), e))
['a', 'aac', 'b', 'c', 'd', 1, True, 1.1, 2, 4, 6L, 35]

Note that different numeric types are being correctly sorted (1<=True<1.1<6L<35)

Solution 5:

You can also use the cmp parm:

c = ['c', 'b', 'd', 'a', 4, 2, 1, 3]

defcompare_function(a, b):
    ifisinstance(a, str) andisinstance(b, int):
        return -1ifisinstance(a, int) andisinstance(b, str):
        return1return cmp(a, b)

c.sort(cmp=compare_function)