How good is startswith?

Question

Is

text.startswith(\'a\')  

better than

text[0]==\'a\'  

?

Knowing text is not empty and we a

Answer 1

text[0] fails if text is an empty string:

IronPython 2.6 Alpha (2.6.0.1) on .NET 4.0.20506.1
Type "help", "copyright", "credits" or "license" for more information.
>>> text = ""
>>> print(text.startswith("a"))
False
>>> print(text[0]=='a')
Traceback (most recent call last):
  File "", line 1, in 
IndexError: index out of range: 0

EDIT: You say you "know" that text is not empty... how confident are you of that, and what would you want to happen if it is empty in reality? If a failure is appropriate (e.g. it means a bug in your code) that would encourage the use of text[0]=='a'.

Other questions:

• How concerned are you about the performance of this? If this is performance critical, then benchmark it on your particular Python runtime. I wouldn't be entirely surprised to find that (say) one form was faster on IronPython and a different one faster on CPython.

• Which do you (and your team) find more readable?