Python: startswith any alpha character

Question

How can I use the startswith function to match any alpha character [a-zA-Z]. For example I would like to do this:

if line.startswith(ALPHA):
    Do Something

score 61 · Accepted Answer · edited Oct 15 '19 at 20:35

61

If you want to match non-ASCII letters as well, you can use str.isalpha:

if line and line[0].isalpha():

edited Oct 15 '19 at 20:35

Boris Verkhovskiy

answered Mar 07 '10 at 10:08

dan04

24

Even shorter: `if line[:1].isalpha():` – Will Hardy Mar 07 '10 at 11:47
@Will What is the difference between your answer and `if line[0].isalpha():` – teggy Mar 07 '10 at 18:57
14

@teggy: The difference is that if line is an empty string, line[:1] will evaluate to an empty string while line[0] will raise an IndexError. – dan04 Mar 07 '10 at 19:36

score 13 · Answer 2 · answered Mar 07 '10 at 10:03

13

You can pass a tuple to startswiths() (in Python 2.5+) to match any of its elements:

import string
ALPHA = string.ascii_letters
if line.startswith(tuple(ALPHA)):
    pass

Of course, for this simple case, a regex test or the in operator would be more readable.

answered Mar 07 '10 at 10:03

efotinis

I did not know that. +1 not for the best answer for this question, but because that is by far the best answer for a ton of my own code. Thank you. – DaveTheScientist May 09 '12 at 21:27

score 9 · Answer 3 · answered Mar 07 '10 at 09:56

9

An easy solution would be to use the python regex module:

import re
if re.match("^[a-zA-Z]+.*", line):
   Do Something

answered Mar 07 '10 at 09:56

Il-Bhima

-1: Using regex is massively overkill for this task. Also you only need to check the first character - this regex will try and match the whole string, which could be very long. – Dave Kirby Mar 07 '10 at 10:12
7

Even if you were forced to use the re module, all you needed was `[a-zA-Z]`. The `^` is a waste of a keystroke (read the docs section about the difference between `search` and `match`). The `+` is a minor waste of time (major if the string has many letters at the start); one letter is enough. The `.*` is a waste of 2 keystrokes and possibly a lot more time. – John Machin Mar 07 '10 at 10:53

score 3 · Answer 4 · answered Mar 07 '10 at 10:08

3

This is probably the most efficient method:

if line != "" and line[0].isalpha():
    ...

answered Mar 07 '10 at 10:08

Dave Kirby

score 0 · Answer 5 · answered Sep 09 '11 at 19:37

0

if line.startswith((chr(x) for x in range(ord('a'), ord('z')+1)+range(ord('A'), ord('Z')+1)):
    # do processsing
    pass

answered Sep 09 '11 at 19:37

shantanoo

score -1 · Answer 6 · answered Mar 07 '10 at 11:20

-1

if you don't care about blanks in front of the string,

if line and line.lstrip()[0].isalpha():

answered Mar 07 '10 at 11:20

ghostdog74

6 Answers6