Python __str__ and __repr__

Both str() and repr() methods in python are used for string representation of a string. But there are little difference between them.

>>> x=”Hello World”
>>> print(x.__str__()) ## More readable for end-user
Hello World
>>> print(x.__repr__()) ## More useful for developer and debugging
‘Hello World’

__str__

1. Make object more readable
2. Invoked by str, print ..etc.
3. str() function by default uses __str__(). If __str__() not found, str() uses __repr__()

class C1:
def __init__(self):
pass
def __repr__(self):
return “{}”.format(self.__class__.__name__)

obj=C1()
print(obj)
print(str(obj))

4. Generates output for end-user

5. Informal string representation

6. Cannot reconstruct object

>>> str1 = “Hi”
>>> str(str1)
‘Hi’
>>> str2 = eval (str(str1))
Traceback (most recent call last):
File “<stdin>”, line 1, in <module>
File “<string>”, line 1, in <module>
NameError: name ‘Hi’ is not defined
>>>

__repr__

1. Invoked when you simply write object’s name on interactive python console and press enter
2. Invoked by repr() function

class C1:
def __init__(self):
pass
def __repr__(self):
return “{}”.format(self.__class__.__name__)

obj=C1()
print(obj) # fallback to __repr__ if no __str__ found
print(repr(obj))

Output:
C1
C1

3. If no __repr__ are there in a class, repr() will simply print the object representation

class C1:
def __init__(self):
pass
def __str__(self):
return “{}”.format(self.__class__.__name__)

obj=C1()
print(obj)
print(repr(obj))

Output:

C1
<__main__.C1 object at 0x7f482dfe8070>

4. Generates output for developer and debugging purposes

5. it shows official string representation

6. We can reconstruct object
>>> str1 = “Hi”
>>> repr(str1)
“‘Hi’”
>>> str2 = eval (repr(str1))
>>> str1 == str2
True