Joost Jacob
I am looking for a function that takes an input string
and a pattern, and outputs a dictionary.
# @param s str, lowercase letters
# @param p str, lowercase and uppercase letters
# @return dict
def fill(s, p):
d = {}
....
return d
String s has characters from the lowercase letters.
String p is a pattern, a string of characters from the
lowercase and uppercase letters. The idea is to match
s with p, where lowercase letters have to match
exactly, and to fill variables (with an uppercase
letter name) with the rest of s. The variables are
collected in a dictionary with the resulting bindings.
A variable that occurs in more than one place in p must
bind to the same substring of s.
Tests:
fill('ab', p='aA'){'A': 'b'} fill('ab', p='Ab'){'A': 'a'} fill('bb', p='Ab') # no match{} fill('aa', p='Aa'){'A': 'a'} fill('aa', p='Ab') # no match{} fill('abb', p='aA'){'A': 'bb'} fill('aba', p='aAa'){'A': 'b'} fill('abb', p='aAa') # no match{} fill('abab', p='aAaA') # A-matches must be equal{'A': 'b'} fill('abac', p='aAaA') # no match{} fill('abac', p='aAaB')
{'A': 'b', 'B': 'c'}
Can you do it? Is trying a solution with a regex a
good idea?
Jul 19 '05 #1
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3 
1231 
Joost Jacob
Oops, the 3rd test should be
fill('bb', p='Aa')
resulting in the empty dict {} because no binding for A can be found.
Jul 19 '05 #2
Kent Johnson
Joost Jacob wrote:
I am looking for a function that takes an input string
and a pattern, and outputs a dictionary.
Here is one way. I won't say it's pretty but it is fairly straightforward and it passes all your tests.
Kent
def fill(s, p):
"""
fill('ab', p='aA'){'A': 'b'}
fill('ab', p='Ab'){'A': 'a'}
fill('bb', p='Aa') # no match{}
fill('aa', p='Aa'){'A': 'a'}
fill('aa', p='Ab') # no match{}
fill('abb', p='aA'){'A': 'bb'}
fill('aba', p='aAa'){'A': 'b'}
fill('abb', p='aAa') # no match{}
fill('abab', p='aAaA') # A-matches must be equal{'A': 'b'}
fill('abac', p='aAaA') # no match{}
fill('abac', p='aAaB')
{'A': 'b', 'B': 'c'}
"""
# If s is longer than p the extra chars of s become part of the
# last item of s
if len(s) > len(p):
ss = list(s[:len(p)])
ss[-1] = ss[-1] + s[len(p):]
s = ss
d = {}
seen = {}
for s1, p1 in zip(s, p):
# Lower case have to map to themselves
if p1.islower() and s1 != p1:
# print 'Non-identity map for %s: %s' % (p1, s1)
return {}
try:
# Check for multiple mappings from p1
old_s = d[p1]
if old_s != s1:
# We saw this s before but the mapping is different
return {}
# We saw this s1, p1 before with the same mapping
continue
except KeyError:
# Check for multiple mappings to p1
if seen.get(s1, p1.lower()) != p1.lower():
return {}
# This is a new mapping
d[p1] = s1
seen[s1] = p1.lower()
# Strip out the lower case mappings
return dict((k, v) for k, v in d.iteritems() if k.isupper())
def _test():
import doctest
doctest.testmod ()
if __name__ == "__main__":
_test()
Jul 19 '05 #3
Paul McGuire
Here's a hybrid solution, using pyparsing to parse your input pattern
string (p), and transforming it into a regexp string. Then uses
re.match using the regexp to process string (s), and then builds a
dictionary from the matched groups.
Download pyparsing at http://pyparsing.sourceforge.net.
-- Paul
=============== ====
import re
from pyparsing import Word,OneOrMore
previousKeys = []
def createUpperKey( s,l,t):
if t[0] not in previousKeys:
ret = "(?P<%s>.*) " % t[0]
previousKeys.ap pend(t[0])
else:
ret = "(?P=%s)" % t[0]
return ret
lowers = "abcdefghijklmn opqrstuvwxyz"
uppers = lowers.upper()
lowerLetter = Word(lowers,max =1)
upperLetter = Word(uppers,max =1).setParseAct ion(createUpper Key)
pattern = OneOrMore( lowerLetter | upperLetter )
def fill(s,p):
# reset keys found in p-patterns
del previousKeys[:]
# create regexp by running pyparsing transform
regexp = pattern.transfo rmString(p) + "$"
# create dict from re-matched groups
match = re.match(regexp ,s)
if match:
ret = dict( [ (k,match.group( k)) for k in previousKeys ] )
else:
ret = dict()
return ret
tests = [
('ab','aA'),
('ab','Ab'),
('bb','Aa'),
('aa','Aa'),
('aa','Ab'),
('abb','aA'),
('aba','aAa'),
('abbba','aAa') ,
('abbbaba','aAa '),
('abb','aAa'),
('abab','aAaA') ,
('abac','aAaA') ,
('abac','aAaB') ,
]
for t in tests:
print t,fill( *t )
=============== =
Gives:
('ab', 'aA') {'A': 'b'}
('ab', 'Ab') {'A': 'a'}
('bb', 'Aa') {}
('aa', 'Aa') {'A': 'a'}
('aa', 'Ab') {}
('abb', 'aA') {'A': 'bb'}
('aba', 'aAa') {'A': 'b'}
('abbba', 'aAa') {'A': 'bbb'}
('abbbaba', 'aAa') {'A': 'bbbab'}
('abb', 'aAa') {}
('abab', 'aAaA') {'A': 'b'}
('abac', 'aAaA') {}
('abac', 'aAaB') {'A': 'b', 'B': 'c'}
Jul 19 '05 #4
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