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String formatting allows us to format a string value before it is sent as an output to the user. In this tutorial, we are going to discuss an important string formatting method, format(). But before we could discuss how to format a string value, we should learn about how to extract a string representation of an object.

Therefore, first we are going to discuss some two important functions, str() and repr(), which allow us to retrieve a string representation of any object.

Next, we are going to discuss the string formatting method, format() and its variations provided by the Python.

Functions/Method	Description
str()	This function formats an object passed to it and returns its human-readable form.
repr()	This function returns an interpreter-readable form of an object passed to it.
format()	This method returns a formatted string value and it is used to format specified value(s) passed to it and insert them inside the string's placeholder. This method is only available to string objects.

• Using the str() function


The str() output function returns a human-readable form(in string) of the object value passed to it.

Example of str() function -

# Python - Example of str() function



# Creating a skeletal class by using the pass keyword
class A:
    pass;

	
# Creating different types of objects
i = 100
s1= 19.567
s2 = 'Hello, world.'
s3 = 'Poliśh'



# Calling str() with an int object.
print(str(i))


# Calling str() with an floating-point object.
print(str(s1))


# Calling str() with a string object.
print(str(s2))


# Calling str() with another string object.
print(str(s3))


# Calling str() by passing it a result of concatenating two string objects
print(str('Hello' + 'Goodbye'))


# Calling str() by passing it two number objects
print(str(100/200.5))


#Creating an object of class A
ob = A()


#Calling str() with the object of class A
print(str(ob))




Output




100
19.567
Hello, world.
Poliśh
HelloGoodbye
0.49875311720698257
<__main__.A object at 0x0000000002ED3E10>


As you can see in the example, we have called the str() function with different types of objects and it has formatted all these object values to a simple human-readable form.





• Using the repr() function


The repr() output function takes an object and returns a format which is read by the interpreter or will throw a SyntaxError. If the repr() function is passed with a string object, it returns it enclosed in single quotes.

Example of repr() function -

# Python - Example of repr() function

# Creating a skeletal class by using the pass keyword
class A:
    pass;

	
	
# Creating different types of objects
i = 100
s1= 19.567
s2 = 'Hello, world.'
s3 = 'Poliśh'



# Calling repr() with an int object.
print(repr(i))


# Calling repr() with an floating-point object.
print(repr(s1))


# Calling repr() with a repring object.
print(repr(s2))


# Calling repr() with another repring object.
print(repr(s3))


# Calling repr() by passing it a result of concatenating two repring objects
print(repr('Hello' + 'Goodbye'))


# Calling repr() by passing it two number object
print(repr(100/200.5))


#Creating an object of class A
ob = A()


#Calling repr() with the object of class A
print(repr(ob))




Output




100
19.567
'Hello, world.'
'Poliśh'
'HelloGoodbye'
0.49875311720698257
<__main__.A object at 0x0000000002EBEEF0>


As you can see in the example, we have called the repr() function with different types of objects and it has formatted all these object values to a form readable by interpreter and all the string objects are enclosed within single quotes.




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• Using the format() method


The format() function can only be called on a string value and it formats the specified value(s) passed to it and insert them inside the string's placeholder. The placeholders are defined by using one or more curly brackets { }.

The brackets { } in a string value are known as format fields, where:
• A bracket could be left blank - If the first bracket is left blank, it is replaced by the first argument passed to the format() method, and if the second bracket is left blank then it is replaced by the second argument passed to the format() method and so on.


• A bracket may contain an integer value - A number in the bracket { } can be used to refer to the index position of an argument passed on calling the format() method, where the first index position is zero. For example - {0} is replaced by the first argument passed to format() method, while {1} is replaced by the second argument passed to the format() method and so on.


• A bracket may contain a name, which refers to an argument with the same name that is passed to the called format() method and the value of this matched argument is placed in the placeholder.


Example of format() function -

# Python - Example of format() function


	
# Creating different types of objects
i = 100
s1= 19.567
s2 = 'never give up'
s3 = 'think positive'



# Calling the format() method of string to format the output
# Index 0 refers to i and index 1 refers to s1
print('{0}, {1}'.format(i, s1))



# Calling the format() method of string to format the output
# Index 0 refers to i and index 1 refers to s1
print('{1}, {0}'.format(i, s1))



# Calling the format() method of string to format the output
# First blank {} refers to the first argument passed to format() method
# Second blank {} refers to the second argument passed to the format() method
print('In life, you should {} and always {}'.format(s2,s3))



# Calling the format() method of string to format the output
# blank {} refers to the argument passed to format() method, which is itself a string
print('{} is blue'.format('Sky'))



# Calling the format() method of string to format the output
# First {} refers to the argument - weather and extracts its value 'hot'
# Second {} refers to the argument - love and extracts its value 'rain' 
print('Today, its a {weather} day and I hope it {love}'.format(weather='hot', love='rain'))



# Calling the format() method of string to format the output
# First blank {} refers to the first argument passed to the format() method
# Second {} refers to the argument - color and extracts its value 'green' 
print('{} are {color}'.format('Grapes', color='green'))




Output




100, 19.567
19.567, 100
In life, you should never give up and always think positive
Sky is blue
Today, its a hot day and I hope it rain
Grapes are green


As you can see in the example, we have called the different variants of format() method using the strings comprising of single or more brackets { }.





• Using format() method with format specifiers


Within the brackets { } of a string, we could use a specific format specifier, which will display a value of a specific argument passed to the format() method in an appropriate matching type.

Syntax to use format specifier :

[index-position]:[width][format-specifier]


where,
• index-position is the index position of the argument passed on calling the format() method.
• width is the width in which the argument passed to format() method will be displayed.
• format-specifier is a specific format-specifier that will be applied on a specific argument passed to the format() method.




Format Specifier	Description
c	to display an argument as a character.
f	to display an argument as a float.
s	to display an argument as a string.
o	to display an argument as an octal.
d	to display an argument as a decimal.
x	to display an argument as a hexadecimal with a lowercase character after 9.
X	to display an argument as a hexadecimal with an uppercase character after 9.





An example of using format specifier with format() function.

# Python - Example of format() function


# Calling the format() method of string to format the output
# using format specifier f i.e. float with first element and width of 2
# because there  was only one argument to format() method, hence we didn't have to specify its index.
print('{:.2f}'.format(10.37489))



# Calling the format() method of string to format the output
# using format specifier f i.e. float with index 0 element and width of 0
# using format specifier f i.e. float with index 1 element and width of 6
print('{0:.0f}, {1:.6f}'.format(10.37489, 19.567))



# Calling the format() method of string to format the output
# Index 0 refers to i and index 1 refers to s1
print('{0:f}, {1:.5f}'.format(10.37489, 19.567))


# Calling the format() method of string to format the output
# using format specifier f i.e. float with index 0 element and width of 2
# using format specifier f i.e. float with index 1 element and width of 5
print('{0:.2f}, {1:.5f}'.format(100,200))



# Calling the format() method of string to format the output
# using format specifier d i.e. int with index 0 element
# using format specifier f i.e. float with index 1 element and width of 4
print('{0:d}, {1:.4f}'.format(100,200))


# Calling the format() method of string to format the output
# using format specifier b i.e. binary, to format the output in binary
print('{0:b}'.format(10))


# Calling the format() method of string to format the output
# using format specifier o i.e. octal, to format the output in octal
print('{0:o}'.format(10))


# Calling the format() method of string to format the output
# using format specifier d i.e. decimal, to format the output in decimal
print('{0:d}'.format(10))


# Calling the format() method of string to format the output
# using format specifier o i.e. hexadecimal, to format the output in hexadecimal
print('{0:X}'.format(10))


# Calling the format() method of string to format the output
# using format specifier o i.e. character, to format the output in character
print('{0:c}'.format(65))



# Calling the format() method of string to format the output
# using format specifier s i.e. string, to format the output in string
print('{0:s}'.format('Hello, how do you do?'))





Output




10.37
10, 19.567000
10.374890, 19.56700
100.00, 200.00000
100, 200.0000
1010
12
10
A
A
Hello, how do you do?



Note : Trying to display a value using the format-specifier of a non-matching type will lead to an error. For example - Trying to convert an integer type object passed to format() method, to a string type or to a float type will throw an error. Let us see some of these format specifiers.






• Using format() method for shifting of a value


Within the brackets { } of a string, we could use a specific format specifier, which will perform a specific type of shifting of an argument passed to format() method.

Syntax to use format specifier :

[index-position]:[shifting-character][width][format-specifier]


where,
• index-position is the index position of an argument passed on calling the format() method.
• shifting-character is the character for a specific type of shifting of an argument passed to format() method.
• width is the width in which an argument passed to format() method will be displayed.
• format-specifier is a specific format-specifier that will be applied on a specific argument passed to the format() method.




Shifting character	Description
<	Left shifts the value.
>	Right shifts the value.
s	Center shifts the value.





An example of using format specifier with format() function.

# Python - Example of format() function


# Calling the format() method of string to format the output
# Setting the width of value to 4
print('{:4}'.format(10))


# Right shifting the value and setting the width to 8
print('This is a {:>8} day'.format('good'))


# Don't have to specify the index of the element when there is only one argument to format()
# Left shifting the value by width 9
print('This is a {:<9} day'.format('good'))



# Right shifting the 1st index element by width 7
# Left shifting the zeroth index value by width 10
print('An {1:>7} a day keeps a {0:<10} away'.format('doctor', 'apple'))



# Right shifting the 1st index value by width 7
# Center shifting the 2nd index value by width 10
# Left shifting the zeroth index value by width 10
print('A {:<7} without laughter {:^10} a day {:>10} !'.format('day', 'is', 'wasted'))



# Left shifting the value by width 7
print('This is a {:<7} day'.format('good'))


# Right shifting the value and setting the width to 7
print('{:>8}'.format(10.567))


# Right shifting the value and setting the width to 10
print('{:<10} '.format(10))



# Left shifting the value and setting the width to 10
print('{:>10} '.format(10))



# Center shifting the value and setting the width to 10
print('{:^10} '.format(10))





Output




  10
This is a     good day
This is a good      day
An   apple a day keeps a doctor     away
A day     without laughter     is     a day     wasted !
This is a good    day
  10.567
10         
        10 
    10    



Note : Without setting a specific value of width, use of shifting-character to shift an object will not result in any change on the output.






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