text: # format string
  def format():
      string = "Smith Brian"
      print(string.upper())
      print(string.isupper())
      print(string.upper().isupper())
  format()
  
  # determine length of string: len()
  def checks():
      print(len("The quick brown fox jumps over the lazy dog"))
      lens = "Lorem Ipsum"
      print(len(lens))
  checks()
   
  ### 4.2 Concatenation, Indexing, and Slicing.
  
  ## String concatenation.
  str_1 = 'The quick brown fox jumps '
  str_2 = 'over the lazy dog.'
  print(str_1 + str_2)
  
  ## String index.
      # Đếm xuôi từ 0 nhưng đếm nhưng đếm ngược từ -1.
  def str_index():
      str = "Smith Brian"
      print(str[0], str[-1], str[0:], str[:-1])
  
      #! index() - determine the location of string.
      print(str.index("i")) #* It'll count from left to right, count 1 value.
      print(str.index("Smith")) #* It started from...
  
      #! lstrip() - remove the whitespace in the left - the same as rstrip().
      strip = "    Smith Brian    "
      rstrip = "Smith Brian    "
      lstrip = "    Smith Brian"
      print(rstrip.rstrip()); print(lstrip.lstrip()); print(strip.strip())
  
      #! replace() - replace string <replace(<root string>, <replace string>).
      print(str.replace("Smith", "Dev."))
  str_index()
  
  ### Determine if a String Starts or Ends With a Particular String
  def somethingelse():
      str = "The quick brown fox jumps over the lazy dog"
      print(str.startswith("The"), str.endswith("Dog"))
  somethingelse()
  
  ##! find a string:
  str_var = "smith_br-macpro16"
  print(str_var.find("16"))
  
  ### TODO
      ##? format()	    It’s used to create a formatted string from the template string and the supplied values.
      ##? split()	        Python string split() function is used to split a string into the list of strings based on a delimiter.
      ##? join()	        This function returns a new string that is the concatenation of the strings in iterable with string object as a delimiter.
      ##? strip()	        Used to trim whitespaces from the string object.
      ##? format_map()	Python string format_map() function returns a formatted version of the string using substitutions from the mapping provided.
      ##? upper()	        We can convert a string to uppercase in Python using str.upper() function.
      ##? lower()	        This function creates a new string in lowercase.
      ##? replace()	    Python string replace() function is used to create a new string by replacing some parts of another string.
      ##? find()	        Python String find() method is used to find the index of a substring in a string.
      ##? translate()	    Python String translate() function returns a new string with each character in the string replaced using the given translation table.
  