strings in sorted order, except group all the strings that begin with 'x' first

Question

Given a list of strings, return a list with the strings in sorted order, except group all the strings that begin with 'x' first.

e.g.

['mix', 'xyz', 'apple', 'xanadu', 'aardvark']

yields

['xanadu', 'xyz', 'aardvark', 'apple', 'mix'].

a=['bbb', 'ccc', 'axx', 'xzz', 'xaa']
a1=['mix', 'xyz','apple', 'xanadu', 'aardvark','xz']
xlist=[]
def sort(s):
    for i in s:
        if i[0]=='x':
            xlist.append(i)
            s.remove(i)
    print sorted(xlist)+sorted(s) 
    del xlist[:]

sort(a)
sort(a1)

---

This code works as long as two list elements which start with x dont come together. i.e I get proper output for list a1 but not for a can you help me understand why!

---

obtained output.

['xzz', 'axx', 'bbb', 'ccc', 'xaa']
['xanadu', 'xyz', 'xz', 'aardvark', 'apple', 'mix'] 

Answer 1

You can use sorted or list.sort with two keys:

l = ['mix', 'xyz', 'apple', 'xanadu', 'aardvark']
sorted(l, key=lambda x: (not x.startswith('x'), x))
['xanadu', 'xyz', 'aardvark', 'apple', 'mix']

where not x.startswith('x') returns bool, which gets sorted in False first. Thus, not x.startswith('x') grabs the strs that start with 'x' and bring them to the front.

Answer 2

You are not suppose to remove from the list while iterating over it, try it with a deep copy:

a=['bbb', 'ccc', 'axx', 'xzz', 'xaa']
a1=['mix', 'xyz','apple', 'xanadu', 'aardvark','xz']
xlist=[]
def sort(s):
    for elem in s[:]:
        if elem.startswith('x'):
           xlist.append(elem)
           s.remove(elem)
    print(sorted(xlist)+sorted(s))
    del xlist[:]

sort(a)
sort(a1)

OUTPUT:

['xaa', 'xzz', 'axx', 'bbb', 'ccc']
['xanadu', 'xyz', 'xz', 'aardvark', 'apple', 'mix']