which is the correct way to sort file names?

which is the correct way to sort file names? the way ls does it or the way sort does it? here, you can see a difference for some of my recent files:
Code:lt2a/phil /home/phil 97> ls -1 ftrgen*.py
ftrgen1.py
ftrgen2.py
ftrgen3.py
ftrgen4.py
ftrgend.py
ftrgenf.py
ftrgen.py
ftrgenrules.py
ftrgent.py
lt2a/phil /home/phil 98> ls -1 ftrgen*.py|sort
ftrgen.py
ftrgen1.py
ftrgen2.py
ftrgen3.py
ftrgen4.py
ftrgend.py
ftrgenf.py
ftrgenrules.py
ftrgent.py
lt2a/phil /home/phil 99>