R.I.B.H.U. Academy^®

Concatenation of Strings and Numbers

    The two strings can simply be joined (concate­nated) by using + (concate­nation operator) or += (concate­nation assignment operator). You should also use " " (a string literal consisting of one blank space within a pair of double/single quotes), for proper displaying the result. Or, you can place a blank (white-) space after or before the first or second operand. (An empty string has no blank space within a pair of double/single quotes.)

first_word = 'Good'
second_word = 'Morning'
full_word = first_word + second_word
print( full_word )   # concat­enate two strings, outputs GoodMorning

word = 'Good'
word += 'Evening'
print( word )   # concatenate two strings, outputs GoodEvening

# The above example is explained herein below:
# You can place string literal directly after += operator.
first_word = 'Good'
second_word = 'Evening'
full_word = first_word           # full_word = 'Good'
full_word += second_word   # full_word = full_word + 'Evening'
print( full_word )   # conca­tenate two strings, outputs GoodEvening

print( 'Hello ' + 'World' )   # Outputs Hello World

print( 'Hello' + ' World' )   # Outputs Hello World

print( 'Hello' + ' ' + 'World' )   # Outputs Hello World

    You can also join (concatenate) two or more strings or other data-type literals, with join(), replace() (which are explained below), and format() methods, etc. (explained in next page). An integer or a float when concatenated (that is, added) to string literal, the numeric value must be first type-casted with str() built-in function, otherwise ERROR will be shown.

    A numeric string (that is, a number enclosed within a pair of double/single quotes) can also be type-casted into an integer data-type or a float data-type, with int() or float() built-in function. When you use input() function to get some numeric value from the user, you have to type-cast that data into an integer or a float, since the input() function always returns an string data-type. But, you don't have to convert the returned value from the input() function to string data-type, when concate­nating to other strings.

day_night = "Midnight"
exact_time = 12

# exact_time = str( 12 )     # You can also type-cast before

# or you can ask the user (public) to enter age
# exact_time = input( "What is your birth time: " )     # type-casting is not needed

print( "My time of birth is " + day_night + " at " + str( exact_time ) + "." )

    While concatenating symbols, such as full-stop, comma, plus sign, minus sign, etc. as string, you should be first assured about the positions as described in above example, that is, when adding full-stop, a blank (white-) space may be added after it, when there is next sentence. Any word or number which would follow some texts, a blank (white-) space should be provided before that word or number, and so on...

Type Casting Strings to Integers, and Concatenation

print( '123' + '654' )   # Outputs 123654

print( int( '123' ) + int( '654' ) )   # Outputs 777

Type Casting Integers to Strings, and Concatenation

print( 123 + 654 )   # Outputs 777

print( str( 123 ) + str( 654 ) )   # Outputs 123654

Using \ Escape Characters

    When you need a single quote or a double quote to be placed in a string literal, you have to use \ (backslash character) before them to escape from closing the string. You can also use alternate pair of double/single quotes when inserting one or more single quotes or double quotes. You can insert \n (new line) (see previous page), \r (carriage return), \t (tab), or \f (line-feed) to get line-break, carriage return, tab, line-feed, respectively inside a string literal.

# my_string = 'Don't rely on floats.'   # SyntaxError: unterminated string literal will be shown because after Don, the string literal is closed.

my_string = 'Don\'t rely on floats.'   # Correct way to insert a single quote.
print( my_string )   # Outputs Don't rely on floats.

# my_mood = "I am "happy" now."   # SyntaxError: invalid syntax will be shown

my_mood = "I am \"happy\" now."   # Correct way to insert one or more double quotes.
print( my_mood )   # Outputs I am "happy" now.

print( "Don't rely on floats." )   # Outputs Don't rely on floats.

print( 'I am "happy" now.' )   # Outputs I am "happy" now.

join()

    You can get help documen­tation, by executing the print( help( str.join ) )   statement. See below table for details. The join() method takes only one argument, therefore, two (or more) strings are provided as items/elements of a list data-type. You don't need to provide blank (white-) spaces within string literals, because the join() method is attached to a sub-string (separator) which will be used in between each item/element of the list.

    The join() and split() methods (see previous page) are used to convert a list to string and vice-versa. These two methods are opposite of each other. It is important to note that syntax of join() method is slightly different from that of split() method.

# Syntax: separator.join( iterable_data )   # iterable_data means list, tuple, dictionary, etc. When comma or other symbol is used as separator, fancy result may be returned, which may not be useful.

# Syntax: string_data.split( separator )   # By default, a blank (white-) space, new line, carriage return, line-feed, are treated as separator. You can also use comma, or other symbol as separator.

first_word = 'Good'
last_word = 'Morning'
print( " ".join( [first_word, last_word] ) )   # concatenate two strings, outputs Good Morning

my_string = "Hello World"
new_list = my_string.split()     # see previous page to split strings
print( new_list )                           # Outputs ['Hello', 'World']

new_string = " ".join( new_list )
print( new_string )                       # Outputs Hello World

    String is a sequence data-type, hence, can be used as iterable_data inside paren­theses of join() method, to get fancy output. However, integers, floats, and other data-types, which are not sequence data-type, cannot be directly used as input-string inside paren­theses.

print( '*'.join( str( 123456 ) ) )   # Outputs 1*2*3*4*5*6

my_string = 'PYTHON'
new_list = '*'.join( my_string )
print( new_list )   # Outputs P*Y*T*H*O*N

modified_list = new_list.split( '*' )
print( modified_list )   # Outputs ['P', 'Y', 'T', 'H', 'O', 'N']

new_string = ''.join( modified_list )   # Here, empty string (without a blank space) is used as separator
print( new_string )   # Outputs PYTHON

replace()

    As name of the method suggest, replace() method is used to replace the old-string to new-string. However, you can also use some place­holder, which can be replaced with some value. Hence, in this way, you can concat­enate some data (string or type-casted to string) into parent string. You can get help documen­tation, by executing the print( help( str.replace) )   statement.

parent_string = 'Hello World'
new_string = parent_string.replace( 'Hello', 'New' )
print( new_string )   # Outputs New World

my_string = 'Hello World'
modified_string = my_string.replace( 'l', 'm', 2 )
print( modified_string )   # Outputs Hemmo World because only first sub-strings two are replaced.