2.4.2 Operations on strings and string methods

The addition of several strings results in their concatenation:

last_name = 'Carlsson'
first_name = 'Johanna'
full_name = first_name + ' ' + last_name
  # returns 'Johanna Carlsson'

Consequently, multiplication by an integer is repeated addition:

game = 2 * 'Yo' # returns 'YoYo'

Multiplication by floating-point or complex numbers is undefined and results in a TypeError.

When strings are compared, lexicographical order applies and the uppercase form precedes the lowercase form of the same letter:

'Anna' > 'Arvi' # returns false 
'ANNA' < 'anna'  # returns true 
'10B' < '11A'    # returns true

Among the variety of string methods, we will mention here only the most important ones:

• Splitting a string: This method generates a list from a string by using a single or multiple blanks as separators. Alternatively, an argument can be given by specifying a particular substring as a separator:

text = 'quod erat demonstrandum'
text.split() # returns ['quod', 'erat', 'demonstrandum']
table = 'Johan;Carlsson;19890327'
table.split(';') # returns ['Johan','Carlsson','19890327']
king = 'CarlXVIGustaf'
king.split('XVI')  # returns ['Carl','Gustaf']

• Joining a list to a string: This is the reverse operation of splitting:

sep = ';'
sep.join(['Johan','Carlsson','19890327'])   
# returns 'Johan;Carlsson;19890327'

• Searching in a string: This method returns the first index in the string, where a given search substring starts:

birthday = '20101210'
birthday.find('10') # returns 2

If the search string is not found, the return value of the method is -1.

• String formatting: This method inserts values of variables or results of expressions into a string. It is so important that we devote the following subsection to it.