Python: Character/String Manipulation

[last updated: 2023-09-05]
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• There is no data type for characters. A single character is simply a string data type with a length of 1.

• Concatenation:
  str1 = "this is a"
  str2 = " test"
  str3 = str1 + str2
  print (str3)
  returns: this is a test

• Get a substring:
  string[start: end: step]
  if step omitted, it defaults to 1
  'start' is the index positions of the first character to be included,
  'end' is the index position of the last character to be included, PLUS 1.
  (This is an approximate specification, because as you can see from the examples below, it gets complicated.)
  eg.
  str1 = "abcdefghijk"
  str1[0:5]
  returns: abcde

  str1[-5:]
  returns: ghijk - ie. the last 5 characters of the string

  str1[1:-4]
  returns: bcdefg - ie. all characters except first char and last 4 chars

  str1[::2] - returns every other character

• Remove characters from the beginning or the end of a string:
  strip() method
  eg.: [some string].strip()[-3:]
  gets the last 3 characters of the string.
  (have not tested, but it appears that...) [some string][-3:] does the same
  however if there is whitespace at the end of the string, the strip() will remove them
• [string1].find([string2] will return -1 if string 2 is not found in string1
  If it is there, the position of the first character (zero-indexed) will be returned.
  eg. string1 = "this string", string2 = "is", string1.find(string2) will return 2
• Slicing:
  for string1 = "say what now"
  string1[4:7] returns "wha"
  it includes the first index, but excludes the last
  string1[:2] returns "sa"
  string1[7:] returns "t now"
  string1[-3:] returns "now"
  string1[-3:][0] returns "n"

• Get number of words in a string:
  a_string = "one two three"
  word_list = a_string. split() Split `a_string` by whitespace.
  number_of_words = len(word_list)
  print(number_of_words)

• Get Nth word in String:
  # initializing string
  test_str = "GFG is for Geeks"

  # printing original string
  print("The original string is : " + test_str)

  # initializing N
  N = 3

  # Get Nth word in String
  # using loop
  count = 0
  res = ""
  for ele in test_str:
  if ele == ' ':
  count = count + 1
  if count == N:
  break
  res = ""
  else :
  res = res + ele

  # printing result
  print("The Nth word in String : " + res)
  Output :

  The original string is : GFG is for Geeks
  The Nth word in String : for

• Convert String to list of words:
  • this worked...
    wordList = inStr.split()
    wordList = inStr.split(" ") - this seemed to do the same ...
  • from stackExchange, I think, but didn't work...
    import re
    mystr = 'This is a string, with words!'
    wordList = re.sub("[^\w]", " ", mystr).split()

• Remove a specific word from a string:
  s = s.replace('papa', '')
• Remove nth word from string:
  • nreplace=1
    my_string="hello my friend"
    words=my_string.split(" ")
    words[nreplace]="your"
    " ".join(words)
  • OR -
    You can replace the 4th list item using
    my_list[3] = "new"
    And then put it back together with
    my_new_string = " ".join(my_list)
  • del inStr[2]
    will delete the 2nd index element
    del inStr[2:4]
    will delete 2nd & 3rd index element

• Join elements of a list into a single string:
  wordList = ['this', 'is', 'a', 'sentence']
  newStr = ' '.join(wordList)

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