String Variations
Question:
I have a string in python and a dictionary of ‘rules’, or possible alterations to the string. For example, one rule might have a key of 'he' and a value of 'e', or a key of 'll' and a value of 'l'.
These rules would mean that any occurrence of “’he’ in my string can be replaced with an 'e', and similarly for 'll' and 'l'.
What I want is to find all variations of my string, given this dictionary of rules. For instance, with the two rules from above and the string 'hello', I would like to return:
['hello', 'ello', 'helo', 'elo']
Any help is appreciated, thanks!
Answers:
Write a recursive function that takes a substring of the input. This function then examines all rules. For each rule that matches, one replacement is done, and the remainder of the string is processed by a recursive call:
def apply_rules(rules, input, start=0):
# First yield the outcome of no applied rules.
yield input[start:]
for match, replace in rules:
# Find the first match for this rule.
index = input.find(match, start)
if index < 0:
# No match -- skip to next one
continue
# Prepare the result of the replacement.
prefix = input[start:index] + replace
# Apply further rules to the rest of the string
# by a recursive call.
for suffix in apply_rules(rules, input, index + len(match)):
yield prefix + suffix
Use it like this:
>>> rules = [('he','e'), ('ll','l'), ('e','ee')]
>>> list(apply_rules(rules, 'hello'))
['hello', 'ello', 'elo', 'helo', 'heello', 'heelo']
Please note that I don’t allow rules to be applied on replaced strings, to prevent cases of infinite results as demonstrated in the comments to this question.
I have a string in python and a dictionary of ‘rules’, or possible alterations to the string. For example, one rule might have a key of 'he' and a value of 'e', or a key of 'll' and a value of 'l'.
These rules would mean that any occurrence of “’he’ in my string can be replaced with an 'e', and similarly for 'll' and 'l'.
What I want is to find all variations of my string, given this dictionary of rules. For instance, with the two rules from above and the string 'hello', I would like to return:
['hello', 'ello', 'helo', 'elo']
Any help is appreciated, thanks!
Write a recursive function that takes a substring of the input. This function then examines all rules. For each rule that matches, one replacement is done, and the remainder of the string is processed by a recursive call:
def apply_rules(rules, input, start=0):
# First yield the outcome of no applied rules.
yield input[start:]
for match, replace in rules:
# Find the first match for this rule.
index = input.find(match, start)
if index < 0:
# No match -- skip to next one
continue
# Prepare the result of the replacement.
prefix = input[start:index] + replace
# Apply further rules to the rest of the string
# by a recursive call.
for suffix in apply_rules(rules, input, index + len(match)):
yield prefix + suffix
Use it like this:
>>> rules = [('he','e'), ('ll','l'), ('e','ee')]
>>> list(apply_rules(rules, 'hello'))
['hello', 'ello', 'elo', 'helo', 'heello', 'heelo']
Please note that I don’t allow rules to be applied on replaced strings, to prevent cases of infinite results as demonstrated in the comments to this question.