assignment to make a Search function

[snow56border]

I am working on an assignment in python. The goal is to make a function with two parameters, one for a string and the other for a pattern. If the pattern appears in the string, the program must return true, or false if otherwise. Also, the pattern can accept *'s to represent any number of characters can appear in between and the pattern is still good.
ex.
matchPat(a*t*r. anteaters)
True
matchPat(a*t*r. albatross)
Ture
matchPat(a*t*r. albatross)
False

I have the function set to look through the string one at a time for a match with the first character of the pattern. If true it dumps that character and letters in the string it looked for.

It goes through good enough, but once I get to the end I get an index error since I am usually passes pattern in as "" which isnt allowed. Problem is when I block that instance all I get for an output is None and not true which is what I need.

I put some print statements up and noticed when I get to the end of pattern and the end of the string, I get a random burp of previous values, so I am guessing something in my recursion is off. Any pointers pros? Oh, and no uses of loops

def matchPat(CH, string):
    print(CH)
    print(string)
    input("")
    if not CH:
        return True
    elif CH[0] == string[0]:
        return matchPat(CH[1:], string[1:])
    elif CH[1] == string[0] or matchPat(CH, string[1:]):
        matchPat(CH[1:], string)
        print(CH)
        print(string)

print(matchPat("a*t*r","anteater"))

[griswolf]

You want to use the re nodule. There are examples of use as well as a full reference. Be aware of the difference between the search and the match methods.

[woooee]

You have to test for a length of 2 or greater, otherwise you get and index error on the [1:]s.

return matchPat(CH[1:], string[1:])
    elif CH[1] == string[0] or matchPat(CH, string[1:]):

Note also that line 10
matchPat(CH[1:], string)
does not catch the return from the matchPat function so the "return True" is never caught. Add some print statements so you can see what is happening with each recursion.

[TrustyTony]

This my try seems to work, I do not know if I am overcomplicating things, but you could compare this to your try and maybe debug the problem:

from __future__ import print_function

def match_pat(CH, mystring):
    print ("%r vs %r" % (CH, mystring))
    if not CH:
        return not mystring
    elif CH == '*':
        return True
    elif not mystring:
        return False
    elif CH[0] == '*':
        return any(match_pat(CH[1:],mystring[index:]) for index in range(len(mystring)))
    else:
        return CH[0] == mystring[0] and match_pat(CH[1:], mystring[1:]) 

pat = 'a*at*r*' 
for word in ("anteater",'albatross','albania'):
    print(word, pat, match_pat(pat,word))
    print('-'*30)

[xhaui]

This my try seems to work, I do not know if I am overcomplicating things, but you could compare this to your try and maybe debug the problem:

from __future__ import print_function

def match_pat(CH, mystring):
    print ("%r vs %r" % (CH, mystring))
    if not CH:
        return not mystring
    elif CH == '*':
        return True
    elif not mystring:
        return False
    elif CH[0] == '*':
        return any(match_pat(CH[1:],mystring[index:]) for index in range(len(mystring)))
    else:
        return CH[0] == mystring[0] and match_pat(CH[1:], mystring[1:]) 

pat = 'a*at*r*' 
for word in ("anteater",'albatross','albania'):
    print(word, pat, match_pat(pat,word))
    print('-'*30)

This code is great and works fine. The only problem is with line 12 I believe it is where you say:

return any(match_pat(CH[1:],mystring[index:]) for index in range(len(mystring)))

Is there any way to change this line so it doesn't use a for loop or the any operator? Both of these are not allowed in the final submission.

[TrustyTony]

You could replace the loop part by appropriate recursion. That is appropriate home work for you to understand how.