1 files changed, 37 insertions, 0 deletions
diff --git a/challenge-275/steven-wilson/python/ch-2.py b/challenge-275/steven-wilson/python/ch-2.py
new file mode 100644
index 0000000000..d215aadbe9
--- /dev/null
+++ b/challenge-275/steven-wilson/python/ch-2.py
@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+
+def replace_digits(string):
+    ''' Given an alphanumeric string, where each character is either a letter
+    or a digit, replace each digit in the given string with the value of the
+    previous letter plus (digit) places.
+    >>> replace_digits('a1c1e1')
+    'abcdef'
+    >>> replace_digits('a1b2c3d4')
+    'abbdcfdh'
+    >>> replace_digits('b2b')
+    'bdb'
+    >>> replace_digits('a16z')
+    'abgz'
+    '''
+    if not string[0].isalpha():
+        raise ValueError('First character of string should be letter.')
+
+    if not string.isalnum():
+        raise ValueError('String should be alphanumeric')
+
+    previous_letter = None
+    result = []
+    for c in string:
+        if c.isdigit():
+            result.append(chr(ord(previous_letter) + int(c)))
+        else:
+            result.append(c)
+            previous_letter = c
+    return "".join(result)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod(verbose=True)