Use of input/raw_input in python 2 and 3 [duplicate]

Question

I would like to set a user prompt with the following question:

save_flag is not set to 1; data will not be saved. Press enter to continue.

input() works in python3 but not python2. raw_input() works in python2 but not python3. Is there a way to do this so that the code is compatible with both python 2 and python 3?

Slur

If you want compatibility you might want to use six. – Fader

Answer 1

Bind raw_input to input in Python 2:

try:
    input = raw_input
except NameError:
    pass

Now input will return a string in Python 2 as well.

---

If you're using six to write 2/3 compatible code then six.input() there points to raw_input() in Python 2 and input() in Python 3.

Tenon

Pylint on Python 2.7 doesn't like it: Redefining built-in 'input' (redefined-builtin) – Nonstandard

Argh... Pylint is both a blessing and a curse. A blessing for n00bs to Python to help guide them in writing Python code; a curse to advanced Python charmers for slapping them for perfectly valid code. I would argue that Pylint is wrong in this case and it sucks to have to uglify your code with a # pylint: disable comment just to make some tool happy. – Laudanum

When I try to use this I get UnboundLocalError: local variable 'input' referenced before assignment when using input afterwards, even when it's running Python 3 – Ureter

@ProQ That's because you're doing this inside a function / class. You need to do it outside, otherwise Python will think you are declaring a local variable, and it will not have a value if there is a NameError. – Jardiniere

The path in six is now six.moves.input. – Scallop

Answer 2

I think the best way to do this is

import six

six.moves.input()

...it'll work across 2 and 3.

Crocodilian

Answer 3

Update: This method only works if you have future installed and the answers above are much better and more generalizable.

From this cheatsheet there is another method that looks cleaner:

# Python 2 and 3:
from builtins import input

Centrosphere

In Python 2: ImportError: No module named builtins – Laudanum

ahh I had the future package installed and didn't realize it. – Centrosphere

This answer is what I do, install the future package and then import from future and also use from builtins import * in every script. – Brume

most modern python training courses provide this code to overcome this problem: if hasattr(__builtins__, 'raw_input'): input = raw_input (2nd line is indented under first). The answer provided here did not work on an Anaconda distribution of iPython 2.7 and I see others reporting issues with this solution as well. This answer should be deleted so people do not try to use it and run into trouble. – Gonorrhea

Oddly enough, I've had issues with EOFError using this method. from six.moves import input seems to work better for me – Pahl

Answer 4

This is because, In python 2, raw_input() accepts everything given to stdin, as a string, where as input() preserves the data type of the given argument (i.e. if the given argument is of type int, then it will remain as int only, but won't be converted to string as in case of raw_input()). That is basically, when input() is used, it takes the arguments provided in stdin as string, and evaluates the same. And this evaluation converts the argument to corresponding type.

# Python 2.7.6
>>> a = raw_input("enter :- ")
enter :- 3
>>> type(a)     # raw_input() converts your int to string
<type 'str'>
>>> a = input("enter :- ")
enter :- 3
>>> type(a)    # input() preserves the original type, no conversion     
<type 'int'> 
>>>

Therefore, while using input() in Python 2, user has to be careful while passing the arguments. If you are passing a string, you need to pass it with quote ( since python recognizes characters inside quote as string). Else NameError will be thrown.

 >>> a = input("enter name :- ")
 enter name :- Derrick
 Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "<string>", line 1, in <module>
 NameError: name 'Derrick' is not defined
 >>> a = input("enter name :- ")
 enter name :- 'Derrick'
 >>> a
 'Derrick'

Whereas, if using raw_input(), you need not worry about the data type while passing the argument as everything it accepts as a string. But yes, inside your code you need to take care of appropriate type conversion.

To avoid this extra care needed for input() in Python 2, it has been removed in Python 3. And raw_input() has been renamed to input() in Python 3. The functionality of input() from Python 2 is no more in Python 3. input() in Python 3 serves what raw_input() was serving in Python 2.

This post might be helpful for a detailed understanding.

Wychelm

-1 although it is a nice explanation, it completely misses the question: Is there a way to do this so that the code is compatible with both python 2 and python 3?. The OP knows about the differences and is interested in a solution to the problem, not the explanation of it. Btw, the functionality of py2 input can be easily recovered with eval(input()) in py3, which makes your last sentences about the functionality, that is no more, obsolet. Yes, there is no single command, but a very simple recovery. – Bailly

DO NOT use eval to replicate Py2 behaviour. That is not the equivalent of input in Py2. Use ast.literal_eval. – Hubbard

Answer 5

Explicitly load the function:

from builtins import input

Then you can use input() in python2 as well as python3.

You may have to install the dependency:

pip install future

Benenson

Answer 6

You can write your code in either python2 and use futurize or in python3 and use pasteurize. This removes the complexity of thinking about compatible code and guarantees good practices.

Regarding this specific question

from builtins import input

Is exactly what the above scripts produce.

Dogear