str() vs repr() in Python

1.7

str() and repr() both are used to get a string representation of object.

  1. Example of str():

    s = 'Hello, Geeks.'
    print str(s)
    print str(2.0/11.0)
    

    Output:

    Hello, Geeks.
    0.181818181818
  2. .

  3. Example of repr():
    s = 'Hello, Geeks.'
    print repr(s)
    print repr(2.0/11.0)
    

    Output:

    'Hello, Geeks.'
    0.18181818181818182

From above output, we can see if we print string using repr() function then it prints with a pair of quotes and if we calculate a value we get more precise value than str() function.

Following are differences:

  • str() is used for creating output for end user while repr() is mainly used for debugging and development. repr’s goal is to be unambiguous and str’s is to be readable. For example, if we suspect a float has a small rounding error, repr will show us while str may not.
  • repr() compute the “official” string representation of an object (a representation that has all information about the abject) and str() is used to compute the “informal” string representation of an object (a representation that is useful for printing the object).
  • The print statement and str() built-in function uses __str__ to display the string representation of the object while the repr() built-in function uses __repr__ to display the object.

Let understand this by an example:-

import datetime
today = datetime.datetime.now()

# Prints readable format for date-time object
print str(today)

# prints the official format of date-time object
print repr(today)     

Output:

2016-02-22 19:32:04.078030
datetime.datetime(2016, 2, 22, 19, 32, 4, 78030)

str() displays today’s date in a way that the user can understand the date and time.

repr() prints “official” representation of a date-time object (means using the “official” string representation we can reconstruct the object).

How to make them work for our own defined classes?
A user defined class should also have a __repr__ if we need detailed information for debugging. And if we think it would be useful to have a string version for users, we create a __str__ function.

# Python program to demonstrate writing of __repr__ and
# __str__ for user defined classes

# A user defined class to represent Complex numbers
class Complex:

    # Constructor
    def __init__(self, real, imag):
       self.real = real
       self.imag = imag

    # For call to repr(). Prints object's information
    def __repr__(self):
       return 'Rational(%s, %s)' % (self.real, self.imag)    

    # For call to str(). Prints readable form
    def __str__(self):
       return '%s + i%s' % (self.real, self.imag)    


# Driver program to test above
t = Complex(10, 20)

print str(t)  # Same as "print t"
print repr(t)

Output:

10 + i20
Rational(10, 20)

This article is contributed by Arpit Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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