I'm having trouble with a program, the program takes one word, and changing one letter at a time, converts that word into the target word. Although, keep in mind that the converted word must be a legal word according to a dictionary of words that I've been given.
I'm having trouble figuring out how to make it recursive. The program has a limit to the amount of steps it must take.
The output needs to be a list. So if the parameters for the function changeling are
changeling("find","lose"), the output should be:
['find','fine','line','lone','lose'].
with my current code:
def changeling(word,target,steps):
holderlist=[]
i=0
if steps<0 and word!=target:
return None
if steps!=-1:
for items in wordList:
if len(items)==len(word):
i=0
if items!=word:
for length in items:
if i==1:
if items[1]==target[1] and items[0]==word[0] and items[2:]==word[2:]:
if items==target:
print "Target Achieved"
holder.list.append(target)
holderlist.append(items)
holderlist.append(changeling(items,target,steps-1))
elif i>0 and i<len(word)-1 and i!=1:
if items[i]==target[i] and items[0:i]==word[0:i] and items[i+1:]==word[i+1:]:
if items==target:
print "Target Achieved"
holderlist.append(items)
holderlist.append(changeling(items,target,steps-1))
elif i==0:
if items[0]==target[0] and items[1:]==word[1:]:
if items==target:
print "Target Achieved"
holderlist.append(items)
holderlist.append(changeling(items,target,steps-1))
elif i==len(word)-1:
if items[len(word)-1]==target[len(word)-1] and items[0:len(word)-1]==word[0:len(word)-1]:
if items==target:
print "Target Achieved"
holderlist.append(items)
holderlist.append(changeling(items,target,steps-1))
else:
return None
i+=1
return holderlist
I receive a messy output:
['fine', ['line', ['lone', ['lose', []]]], 'fond', []]
I get the answer I wanted, but I'm not sure how to a)clean it up, by not having lists within lists. and b)fond appears, because when find is called it gives fine and fond, fine is the one that ends up with the target word, and fond fails, but I'm not sure how to get rid of it once I've appended it to the holderlist.
Any help would be appreciated.
Cheers.
I'm not completely convinced that using extend instead of append will solve all your problems, because it seems like that may not account for making a change that does not lead to solving the word and requires backtracking.
If it turns out I am correct and the other answers don't end up working, here is a recursive function that will convert your current result into what you are looking for:
def flatten_result(nested_list, target):
if not nested_list:
return None
for word, children in zip(nested_list[::2], nested_list[1::2]):
if word == target:
return [word]
children_result = flatten_result(children, target)
if children_result:
return [word] + children_result
return None
>>> result = ['fine', ['line', ['lone', ['lose', []]]], 'fond', []]
>>> flatten_result(result, 'lose')
['fine', 'line', 'lone', 'lose']
If you're trying to add a list to a list, you probably want extend rather than append.
http://docs.python.org/library/stdtypes.html#mutable-sequence-types
Here's an alternative implementation. It doesn't use recursion, but instead permutations. It's been rewritten to pass the wordlist rather than rely on the global wordlist, which should make it more portable. This implementation relies strictly on generators, too, which ensures a smaller memory footprint than expanding lists (as in the extend/append solution)
import itertools
somelists = [['find','fine','line','lone','lose'],
['bank','hank','hark','lark','lurk'],
['tank','sank','sink','sing','ding']]
def changeling(word, target, wordlist):
def difference(word, target):
return len([i for i in xrange(len(word)) if word[i] != target[i]])
for length in xrange(1, len(wordlist) + 1):
for possibilities in [j for j in itertools.permutations(wordlist, length) if j[0] is word and j[-1] is target]:
#computes all permutations and discards those whose initial word and target word don't match parameters
if all(difference(possibilities[i], possibilities[i+1]) == 1 for i in xrange(0, len(possibilities) - 1)):
#checks that all words are exactly one character different from previous link
return possibilities
#returns first result that is valid; this can be changed to yield if you wish to have all results
for w in somelists:
print "from '%s' to '%s' using only %s" % (w[-2], w[0], w)
print changeling(w[-2], w[0], w)
print
w[-2], w[0] can be modified/replaced to match any words you choose
Related
Trying to reiterate backward the codes so as to find common suffix of the entered array of words say:
LongestCommonSuffix(['celebration', 'opinion', 'decision', 'revision'])
To get "ion" as output
This gives me the Longest Common Prefix BUT I need to change the loop to do the same but from the end of each word in the entered list without using Binary manipulation just LOOPING
def fun(strs):
res = ''
for i in range(len(strs[0])):
for s in strs:
if i == len(s) or s[i] != strs[0][i]:
return res
res += strs[0][i]
return res
You could create a variable common_suffix, make that equal to the first word, and then for each next word check if that word ends with that common suffix. If it doesn't, the common suffix is invalid, so try to shorten it until it does.
In code:
def LongestCommonSuffix(strs):
common_suffix = strs[0]
for next_word in strs[1:]:
while not next_word.endswith(common_suffix):
common_suffix = common_suffix[1:]
return common_suffix
print(LongestCommonSuffix(['celebration', 'opinion', 'decision', 'revision']))
This prints ion.
Note that this code works because common_suffix would be an empty string if all words are completely different. And each word ends with an empty string (for example 'test'.endswith('') is True), so the while loop will always quit.
You could add additional logic to break from the loop earlier, but if performance is not critical, I would stick with the simple code :-)
This is my code, but it doesn't work. It should read text from the console, split it into words and distribute them into 3 lists and use separators between them.
words = list(map(str, input().split(" ")))
lowercase_words = []
uppercase_words = []
mixedcase_words = []
def split_symbols(list):
from operator import methodcaller
list = words
map(methodcaller(str,"split"," ",",",":",";",".","!","( )","","'","\\","/","[ ]","space"))
return list
for word in words:
if words[word] == word.lower():
words[word] = lowercase_words
elif words[word] == word.upper():
words[word] = uppercase_words
else:
words[word] = mixedcase_words
print(f"Lower case: {split_symbols(lowercase_words)}")
print(f"Upper case: {split_symbols(uppercase_words)}")
print(f"Mixed case: {split_symbols(mixedcase_words)}")
There are several issues in your code.
1) words is a list and word is string. And you are trying to access the list with the index as string which will throw an error. You must use integer for indexing a list. In this case, you don't even need indexes.
2) To check lower or upper case you can just do, word == word.lower() or word == word.upper(). Or another approach would be to use islower() or isupper() function which return a boolean.
3) You are trying to assign an empty list to that element of list. What you want is to append the word to that particular list. You want something like lowercase_words.append(word). Same for uppercase and mixedcase
So, to fix this two issues you can write the code like this -
for word in words:
if word == word.lower(): # same as word.islower()
lowercase_words.append(word)
elif word == word.upper(): # same as word.isupper()
uppercase_words.append(word)
else:
mixedcase_words.append(word)
My advice would be to refrain from naming variable things like list. Also, in split_words() you are assigning list to words. I think you meant it other way around.
Now I am not sure about the "use separators between them" part of the question. But the line map(methodcaller(str,"split"," ",",",":",";",".","!","( )","","'","\\","/","[ ]","space")) is definitely wrong. map() takes a function and an iterable. In your code the iterable part is absent and I think this where the input param list fits in. So, it may be something like -
map(methodcaller("split"," "), list)
But then again I am not sure what are you trying to achieve with that many seperator
I´ve searched for other "string index out of range" cases, but they were not useful for me, so I wanted to search for help here.
The program has to do this: "Write a function kth_word(s, k) that given a string s and an integer k≥ 1 returns the kth word in string s. If s has less than k words it returns the empty string. We assume all characters of s are letters and spaces. Warning: do not use the split string method."
Here is my code:
def kth_word(s, k):
new =""
word_count = 0
for i in range(0, len(s)):
if s[i] == " " and s[i+1] != " ":
word_count+=1
#try to find how many characters to print until the space
if word_count == k-1:
while i!= " " and i<=len(s): #if it is changed to i<len(s), the output is strange and wrong
new+=s[i]
i=i+1
print(new) #check how new is doing, normally works good
return new
print(kth_word('Alea iacta est', 2))
(I tried my best to implement the code in a right way, but i do not know how)
And depending on the place where you live return new it gives or an error or just an empty answer
You iterate from 0 to len(s)-1 in your first for loop, but you're addressing i+1 which, on the last iteration, is len(s).
s[len(s)] is an IndexError -- it is out of bounds.
Additionally your while loop is off-by-one.
while i!= " " and i<=len(s):
# do something referencing s[i]
Your first condition makes no sense (i is a number, how could it be " "?) and your second introduces the same off-by-one error as above, where i is maximally len(s) and s[len(s)] is an error.
Your logic is a bit off here, too, since you're wrapping this inside the for loop which is already referencing i. This appears to be a takewhile loop, but isn't really doing that.
Warning: do not use the split string method.
So groupby / islice from itertools should work:
from itertools import groupby, islice
def kth_word(s, k):
g = (j for i, j in groupby(s, key=lambda x: x==' ') if not i)
return ''.join(next(islice(g, k-1, k), ''))
words = 'Alea iacta est'
res = kth_word(words, 2) # 'est'
We handle StopIteration errors by setting the optional parameter in next to ''.
You're not allowed to use str.split. If you could, the answer would just be:
def kth_word(s, k):
return s.split()[k]
But if you could write a function that does the same thing str.split does, you could call that instead. And that would certainly show that you understand everything the assignment was testing for—how to loop over strings, and do character-by-character operations, and so on.
You can write a version with only the features of Python usually taught in the first week:
def split(s):
words = []
current = ''
for ch in s:
if ch.isspace():
if current:
words.append(current)
current = ''
else:
current += ch
if current:
words.append(current)
return words
If you know additional Python features, you can improve it in a few ways:
Build current as a list instead of a str and ''.join it.
Change those append calls to yield so it splits the string lazily (even better than str.split).
Use str.find or str.index or re.search to find the next space instead of searching character by character.
Abstract out the space-finding part into a general-purpose generator—or, once you realize what you want, find that function in itertools.
Add all of the features we're missing from str.split, like the ability to pass a custom delimiter instead of breaking on any whitespace.
But I think even the basic version—assuming you understand it and can explain how it works—ought to be enough to get an A on the assignment.
And, more importantly, you're practicing the best way to solve problems: reduce them to simpler problems. split is actually easier to write than kth_word, but once you write split, kth_word becomes trivial.
You actually have at least five problems here, and you need to fix all of them.
First, as pointed out by Adam Smith, this is wrong:
for i in range(0, len(s)):
if s[i] == " " and s[i+1] != " ":
This loops with i over all the values up to but not including len(s), which is good, but then, if s[i] is a space, it tries to access s[i+1]. So, if your string ended with a space, you would get an IndexError here.
Second, as ggorlen pointed out in a comment, this is wrong:
while i!= " " and i<=len(s):
new+=s[i[]
When i == len(s), you're going to try to access s[i], which will be an IndexError. In fact, this is the IndexError you're seeing in your example.
You seem to realize that's a problem, but refuse to fix it, based on this comment:
#if it is changed to i<len(s), the output is strange and wrong
Yes, the output is strange and wrong, but that's because fixing this bug means that, instead of an IndexError, you hit the other bugs in your code. It's not causing those bugs.
Next, you need to return new right after doing the inner loop, rather than after the outer loop. Otherwise, you add all of the remaining words rather than just the first one, and you add them over and over, once per character, instead of just adding them once.
You may have been expecting that doing that i=i+1 would affect the loop variable and skip over the rest of the word, but (a) it won't; the next time through the for it just reassigns i to the next value, and (b) that wouldn't help anyway, because you're only advancing i to the next space, not to the end of the string.
Also, you're counting words at the space, but then you're iterating from that space until the next one. Which means (except for the first word) you're going to include that space as part of the word. So, you need to do an i += 1 before the while loop.
Although it would probably be a lot more readable to not try to reuse the same variable i, and also to use for instead of while.
Also, your inner loop should be checking s[i] != " ", not i!=" ". Obviously the index, being a number, will never equal a space character.
Without the previous fix, this would mean you output iacta est
with an extra space before it—but with the previous fix, it means you output nothing instead of iacta.
Once you fix all of these problems, your code works:
def kth_word(s, k):
word_count = 0
for i in range(0, len(s) - 1):
if s[i] == " " and s[i+1] != " ":
word_count+=1
#try to find how many characters to print until the space
if word_count == k-1:
new =""
j = i+1
while j < len(s) and s[j] != " ":
new+=s[j]
j = j+1
print(new) #check how new is doing, normally works good
return new
Well, you still have a problem with the first word, but I'll leave it to you to find and fix that one.
Your use of the variable 'i' in both the for loop and the while loop was causing problems. using a new variable, 'n', for the while loop and changing the condition to n < len(s) fixes the problem. Also, some other parts of your code required changing because either they were pointless or not compatible with more than 2 words. Here is the fully changed code. It is explained further down:
def kth_word(s, k):
new = ""
word_count = 0
n = 0
for i in range(0, len(s) - 1):
if s[i] == " " and s[i + 1] != " ":
word_count += 1
#try to find how many characters to print until the space
if word_count < k:
while n < len(s): #if it is changed to i<len(s), the output is strange and wrong
new+=s[n]
n += 1
print(new) #check how new is doing, normally works good
return new
print(kth_word('Alea iacta est', 2))
Explanation:
As said in Adam Smith's answer, 'i' is a number and will never be equal to ' '. That part of the code was removed because it is always true.
I have changed i = i + 1 to i += 1. It won't make much difference here, but this will help you later when you use longer variable names. It can also be used to append text to strings.
I have also declared 'n' for later use and changed for i in range(0, len(s)): to for i in range(0, len(s) - 1): so that the for loop can't go out of range either.
if word_count == k-1: was changed to if word_count < k: for compatibility for more words, because the former code only went to the while loop when it was up to the second-last word.
And finally, spaces were added for better readability (This will also help you later).
def sucontain(A):
C = A.split()
def magic(x):
B = [C[i]==C[i+1] for i in range(len(C)-1)]
return any(B)
N = [x for x in C if magic(x)]
return N
Phrase = "So flee fleeting candy can and bandage"
print (sucontain(Phrase))
The goal of this function is to create a list of the words that are inside of each successive word. For example the function would take the string ""So flee fleeting candy can and bandage" as input and return ['flee', 'and'] because flee is inside fleeting (the next word) and 'and' is inside 'bandage'. If no cases like these are found, an empty list [] should be returned. My code right now is returning [] instead of ['flee', 'and']. Can someone point out what I'm doing wrong? thank you
Just pair the consecutive words, then it becomes an easy list comprehension…
>>> s = "So flee fleeting candy can and bandage"
>>> words = s.split()
>>> [i for i, k in zip(words, words[1:]) if i in k]
['flee', 'and']
There is definitely something wrong with your magic function. It accepts x as an argument but doesn't use it anywhere.
Here is an alternate version that doesn't use an additional function:
def sucontain(A):
C = A.split()
return [w for i, w in enumerate(C[:-1]) if w in C[i+1]]
The enumerate() function allows us to loop over the indices and the values together, which makes it very straight forward to perform the test. C[i+1] is the next value and w is the current value so w in C[i+1] checks to see if the current value is contained in the next value. We use C[:-1] to make sure that we stop one before the last item, otherwise C[i+1] would result in an IndexError.
Looking ahead can be problematic. Instead of testing whether the current word is in the next one, check to see whether the previous word is in the current one. This almost always makes things simpler.
Also, use descriptive variable names instead of C and A and x and B and N and magic.
def succotash(text): # okay, so that isn't very descriptive
lastword = " " # space won't ever be in a word
results = []
for currentword in text.split():
if lastword in currentword:
results.append(currentword)
lastword = currentword
return results
print succotash("So flee fleeting candy can and bandage")
I'm just starting to learn python and I have this exercise that's puzzling me:
Create a function that can pack or unpack a string of letters.
So aaabb would be packed a3b2 and vice versa.
For the packing part of the function, I wrote the following
def packer(s):
if s.isalpha(): # Defines if unpacked
stack = []
for i in s:
if s.count(i) > 1:
if (i + str(s.count(i))) not in stack:
stack.append(i + str(s.count(i)))
else:
stack.append(i)
print "".join(stack)
else:
print "Something's not quite right.."
return False
packer("aaaaaaaaaaaabbbccccd")
This seems to work all proper. But the assignment says that
if the input has (for example) the letter a after b or c, then
it should later be unpacked into it's original form.
So "aaabbkka" should become a3b2k2a, not a4b2k2.
I hence figured, that I cannot use the "count()" command, since
that counts all occurrences of the item in the whole string, correct?
What would be my options here then?
On to the unpacking -
I've thought of the basics what my code needs to do -
between the " if s.isalpha():" and else, I should add an elif that
checks whether or not the string has digits in it. (I figured this would be
enough to determine whether it's the packed version or unpacked).
Create a for loop and inside of it an if sentence, which then checks for every element:
2.1. If it has a number behind it > Return (or add to an empty stack) the number times the digit
2.2. If it has no number following it > Return just the element.
Big question number 2 - how do I check whether it's a number or just another
alphabetical element following an element in the list? I guess this must be done with
slicing, but those only take integers. Could this be achieved with the index command?
Also - if this is of any relevance - so far I've basically covered lists, strings, if and for
and I've been told this exercise is doable with just those (...so if you wouldn't mind keeping this really basic)
All help appreciated for the newbie enthusiast!
SOLVED:
def packer(s):
if s.isalpha(): # Defines if unpacked
groups= []
last_char = None
for c in s:
if c == last_char:
groups[-1].append(c)
else:
groups.append([c])
last_char = c
return ''.join('%s%s' % (g[0], len(g)>1 and len(g) or '') for g in groups)
else: # Seems to be packed
stack = ""
for i in range(len(s)):
if s[i].isalpha():
if i+1 < len(s) and s[i+1].isdigit():
digit = s[i+1]
char = s[i]
i += 2
while i < len(s) and s[i].isdigit():
digit +=s[i]
i+=1
stack += char * int(digit)
else:
stack+= s[i]
else:
""
return "".join(stack)
print (packer("aaaaaaaaaaaabbbccccd"))
print (packer("a4b19am4nmba22"))
So this is my final code. Almost managed to pull it all off with just for loops and if statements.
In the end though I had to bring in the while loop to solve reading the multiple-digit numbers issue. I think I still managed to keep it simple enough. Thanks a ton millimoose and everyone else for chipping in!
A straightforward solution:
If a char is different, make a new group. Otherwise append it to the last group. Finally count all groups and join them.
def packer(s):
groups = []
last_char = None
for c in s:
if c == last_char:
groups[-1].append(c)
else:
groups.append([c])
last_char = c
return ''.join('%s%s'%(g[0], len(g)) for g in groups)
Another approach is using re.
Regex r'(.)\1+' can match consecutive characters longer than 1. And with re.sub you can easily encode it:
regex = re.compile(r'(.)\1+')
def replacer(match):
return match.group(1) + str(len(match.group(0)))
regex.sub(replacer, 'aaabbkka')
#=> 'a3b2k2a'
I think You can use `itertools.grouby' function
for example
import itertools
data = 'aaassaaasssddee'
groupped_data = ((c, len(list(g))) for c, g in itertools.groupby(data))
result = ''.join(c + (str(n) if n > 1 else '') for c, n in groupped_data)
of course one can make this code more readable using generator instead of generator statement
This is an implementation of the algorithm I outlined in the comments:
from itertools import takewhile, count, islice, izip
def consume(items):
from collections import deque
deque(items, maxlen=0)
def ilen(items):
result = count()
consume(izip(items, result))
return next(result)
def pack_or_unpack(data):
start = 0
result = []
while start < len(data):
if data[start].isdigit():
# `data` is packed, bail
return unpack(data)
run = run_len(data, start)
# append the character that might repeat
result.append(data[start])
if run > 1:
# append the length of the run of characters
result.append(str(run))
start += run
return ''.join(result)
def run_len(data, start):
"""Return the end index of the run of identical characters starting at
`start`"""
return start + ilen(takewhile(lambda c: c == data[start],
islice(data, start, None)))
def unpack(data):
result = []
for i in range(len(data)):
if data[i].isdigit():
# skip digits, we'll look for them below
continue
# packed character
c = data[i]
# number of repetitions
n = 1
if (i+1) < len(data) and data[i+1].isdigit():
# if the next character is a digit, grab all the digits in the
# substring starting at i+1
n = int(''.join(takewhile(str.isdigit, data[i+1:])))
# append the repeated character
result.append(c*n) # multiplying a string with a number repeats it
return ''.join(result)
print pack_or_unpack('aaabbc')
print pack_or_unpack('a3b2c')
print pack_or_unpack('a10')
print pack_or_unpack('b5c5')
print pack_or_unpack('abc')
A regex-flavoured version of unpack() would be:
import re
UNPACK_RE = re.compile(r'(?P<char> [a-zA-Z]) (?P<count> \d+)?', re.VERBOSE)
def unpack_re(data):
matches = UNPACK_RE.finditer(data)
pairs = ((m.group('char'), m.group('count')) for m in matches)
return ''.join(char * (int(count) if count else 1)
for char, count in pairs)
This code demonstrates the most straightforward (or "basic") approach of implementing that algorithm. It's not particularly elegant or idiomatic or necessarily efficient. (It would be if written in C, but Python has the caveats such as: indexing a string copies the character into a new string, and algorithms that seem to copy data excessively might be faster than trying to avoid this if the copying is done in C and the workaround was implemented with a Python loop.)