repr() , str() , eval() in python

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repr() stands for representation and its a “formal” representation ..where str() stands for “informal” way..

Ref# http://docs.python.org/2/reference/datamodel.html

object.__repr__(self)

    Called by the repr() built-in function and by string conversions (reverse quotes) to compute the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form <...some useful description...> should be returned. The return value must be a string object. If a class defines __repr__() but not __str__(), then __repr__() is also used when an “informal” string representation of instances of that class is required.

    This is typically used for debugging, so it is important that the representation is information-rich and unambiguous.

object.__str__(self)

    Called by the str() built-in function and by the print statement to compute the “informal” string representation of an object. This differs from __repr__() in that it does not have to be a valid Python expression: a more convenient or concise representation may be used instead. The return value must be a string object.



In short what "repr()" give us is the same way python think or represent that object .. for str() I would say more human readable form..


For ex: 

>>> import datetime
>>> datetime.datetime.now()
datetime.datetime(2014, 1, 9, 20, 42, 13, 58580)
>>> repr(datetime.datetime.now())
'datetime.datetime(2014, 1, 9, 20, 42, 21, 598036)'
>>> str(datetime.datetime.now())
'2014-01-09 20:42:32.587526'
>>> 


'eval(source[, globals[, locals]])

It evaluate the source in the context of globals and locals. The source may be a string representing a Python expression nor a code object as returned by compile().
The globals must be a dictionary and locals can be any mapping, defaulting to the current globals and locals.If only globals is given, locals defaults to it.'

If you input repr() output as a source for "eval()" , you get the object back..

>>> x = repr(datetime.datetime.now())
>>> x
'datetime.datetime(2014, 1, 9, 20, 49, 45, 157694)'
>>> eval(x)
datetime.datetime(2014, 1, 9, 20, 49, 45, 157694)
>>> 

[Humble]

repr() function can be used to convert an integer to a string..

>>> type(100)
<type 'int'>
>>> type(repr(100))
<type 'str'>
>>> repr(100)
'100'
>>> 

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