🏣 Clean up for arxiv

book/ebook_src/builtin_structures/permutations_alphanumeric.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+''' Write code to generate all possible case permutations of a given
+lower-cased string
+'''
+
+def alpha_permutation(string):
+    '''
+    >>> alpha_permutation('0ab')
+    ['0Ab', '0Ab', '0ab', '0ab', '0Ba', '0Ba', '0ba', '0ba', 'ab0', 'a0b', 'a0b', 'b0a', 'b0a', 'ba0']
+    >>> alpha_permutation('')
+    ''
+    '''
+
+    if len(string) < 2:
+        return string
+
+    result = []
+
+    for i, c in enumerate(string):
+        rest =  string[i+1:] + string[:i]
+        for cc in alpha_permutation(rest):
+            if cc.isalpha():
+                result.append(c.upper() + cc)
+            result.append(c + cc)
+
+    return result
+
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+