Core Python Programming (2nd Edition)

Tests for identifier validity. First symbol must be alphabetic and remaining symbols must
be alphanumeric. This tester program only checks identifiers that are at least two
characters in length.
1 #!usr/bin/env python
2
3 import string
4
5 alphas = string.letters + '_'
6 nums = string.digits
7
8 print 'Welcome to the Identifier Checker v1.0'
9 print 'Testees must be at least 2 chars long.'
10 myInput = raw_input('Identifier to test? ')
11
12 if len(myInput) > 1:
13
14 if myInput[0] not in alphas:
15 print '''invalid: first symbol must be
16 alphabetic'''
17 else:
18 for otherChar in myInput[1:]:
19
20 if otherChar not in alphas + nums:
21 print '''invalid: remaining
22 symbols must be alphanumeric'''
23 break
24 else:
25 print "okay as an identifier"
The example also shows use of the string concatenation operator ( + ) introduced later in this section.
Running this script several times produces the following output:
$ python idcheck.py
Welcome to the Identifier Checker v1.0
Testees must be at least 2 chars long.
Identifier to test? counter
okay as an identifier
$
$ python idcheck.py
Welcome to the Identifier Checker v1.0
Testees must be at least 2 chars long.
Identifier to test? 3d_effects
invalid: first symbol must be alphabetic
Let us take apart the application line by line.
Lines 36
Import the string module and use some of the predefined strings to put together valid alphabetic and