A bunch of Code Wars challenges I have done. Frist function is mine, second is best voted answer.

countLettersAndDigits.py

'''
create a method that can determine how many letters and digits are in a given string.

Example:

"hel2!lo" --> 6
"wicked .. !" --> 6
"!?..A" --> 1
'''

def count_letters_and_digits(s):
    word = [text for text in s if text.isalpha() or text.isdigit()]
    return len(word)

#################
# Best Solution #
#################
def count_letters_and_digits(s):
    return isinstance(s, str) and sum(map(str.isalnum, s))

delOccurences.py

'''
Delete occurrences of an element if it occurs more than n times.
Example:
  delete_nth ([1,1,1,1],2) # return [1,1]

  delete_nth ([20,37,20,21],1) # return [20,37,21]
'''

def delete_nth(order,max_e):
    for index in range(len(order)-1, 1, -1):
        if (order.count(order[index])) > max_e:
            del order[index]
    return order
  
#################
# Best Solution #
#################
def delete_nth(order,max_e):
    ans = []
    for o in order:
        if ans.count(o) < max_e: ans.append(o)
    return ans

extractDomain.py

import re
def extract_domain(url):
    print url.split("//")[-1].split("www.")[-1].split(".")[0]
    print re.search('(https?://)?(www\d?\.)?(?P<name>[\w-]+)\.', url).group('name')

extract_domain('www.xakep.ru')
extract_domain('http://thecodeinn.blogspot.com/2013/07/tutorial-pyqt-digital-clock.html')
extract_domain('https://www.quora.com/How-do-I-extract-only-the-domain-name-from-an-URL')

highestRankedNumber.py

def highest_rank(arr):
    highestValue = {}
    for num in arr:
        highestValue.update({arr.count(num): num})

    return highestValue.get(max(highestValue.keys()))

mexicanWave.py

'''
Example:
  wave("hello") => ["Hello", "hEllo", "heLlo", "helLo", "hellO"]
'''

def wave(str):

    # output = []
    #
    # for num in range(len(str)):
    #     if str[num] != ' ':
    #         output.append((str[:num].lower() + str[num:].capitalize()))
    #
    # return output

    return [(str[:num].lower() + str[num:].capitalize()) for num in range(len(str)) if str[num] != ' ']
  
#################
# Best Solution #
#################
def wave(str):
    return [str[:i] + str[i].upper() + str[i+1:] for i in range(len(str)) if str[i].isalpha()]

stringIncrementer.py

import re

def increment_string(strng):
    
    # If strng is empty return 1.
    try:
        checkString = strng[-1].isdigit()
    except IndexError:
        return '1'
    
    # If the string already ends with a number, the number should be incremented by 1.
    if checkString is True:
        # Get num from end of string.
        fullNum = re.search(r'\d+$', strng).group(0)
        length = len(fullNum)
        num = int(fullNum)+1
        finalNum = ("%0"+"%dd" % length) % num
        # Remove the found ending number from the string.
        stringBit = strng.replace(fullNum, "", 1)
        # Return string with new number on the end.
        return stringBit + str(finalNum)
    # If the string does not end with a number. the number 1 should be appended to the new string.
    else:
        return strng + '1'

#################
# Best solution #
#################
def increment_string(strng):
    head = strng.rstrip('0123456789')
    tail = strng[len(head):]
    if tail == "": return strng+"1"
    return head + str(int(tail) + 1).zfill(len(tail))

testing1-2-3.py

'''
Write a function which takes a list of strings and returns each line prepended by the correct number.

The numbering starts at 1. The format is n: string. Notice the colon and space in between.

Examples:

number([]) # => []
number(["a", "b", "c"]) # => ["1: a", "2: b", "3: c"]
'''

def number(lines):
    return ["%s: %s" % (str(index+1), lines[index]) for index in range(len(lines))]
  
#################
# Best Solution #
#################
def number(lines):
  return ['%d: %s' % v for v in enumerate(lines, 1)]