AbhinavVutukuri AbhinavVutukuri - 2 months ago 6
Python Question

str() vs repr() functions in python 2.7.5

what is the difference between

str()
and
repr()
functions in python 2.7.5?

Explanation on python.org:


The
str()
function is meant to return representations of values which are fairly human-readable, while
repr()
is meant to generate
representations which can be read by the interpreter (or will force a
SyntaxError
if there is no equivalent syntax)


But it wasn't clear for me.

some examples:

>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'" # repr is giving an extra double quotes
>>> str(1.0/7.0)
'0.142857142857'
>>> repr(1.0/7.0)
'0.14285714285714285' # repr is giving value with more precision


so I want to know the following


  1. When should I use
    str()
    and when should I use
    repr()
    ?

  2. In which cases I can use either of them?

  3. What can
    str()
    do which
    repr()
    can't?

  4. What can
    repr()
    do which
    str()
    can't?


Answer

When should i use str() and when should i use repr() ?

Almost always use str() when creating output for end users.

repr() is mainly useful for debugging and exploring. For example, if you suspect a string has non printing characters in it, or a float has a small rounding error, repr() will show you; str() may not.

repr() can also be useful for generating literals to paste into your source code. It can also be used for persistence (with ast.literal_eval or eval), but this is rarely a good idea--if you want editable persisted values, something like JSON or YAML is much better, and if you don't plan to edit them, use pickle.

2.In which cases i can use either of them ?

Well, you can use them almost anywhere. You shouldn't generally use them except as described above.

3.What can str() do which repr() can't ?

Give you output fit for end-user consumption--not always (e.g., str(['spam', 'eggs']) isn't likely to be anything you want to put in a GUI), but more often than repr().

4.What can repr() do which str() can't

Give you output that's useful for debugging--again, not always (the default for instances of user-created classes is rarely helpful), but whenever possible.

And sometimes give you output that's a valid Python literal or other expression--but you rarely want to rely on that except for interactive exploration.

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