[Tutor] renaming input works intermittently

[Peter Otten]

Jim Mooney wrote:

> When I tried a simple rename of input, it worked - in python 2.7 and
> python 3.3
> 
> import sys
> if int(sys.version[0]) < 3:
>     input = raw_input
> 
> x = input('type something ')
> print(x)  # this works in both Py versions
> 
> But when I tried that in my numbers program, I got an error:
> UnboundLocalError: local variable 'input' referenced before assignment
> for the below:
> 
>         try:
>             if int(sys.version[0]) < 3:
>                 input = raw_input
>             numbers_str = original = input('Enter a positive'
> 'integer, space separated if desired.') # error occurs here
> 
> Oddly, the error only occurs in Python 3.3 - the above works in Python 2.7
> 
> Here it is, where I run it from the dos box. Fails in Py3 on the first
> run, works in Py2 on the second run

If you want to assign inside a function you can just pick an unused name:

def foo():
    if sys.version_info.major < 3: # sys.version_info[0] to support
                                   # versions below 2.7
        safe_input = raw_input
    else:
        safe_input = input
    numstr = safe_input("Enter a positive integer: ")
    ...

Personally I prefer to test for a feature rather than the version:

def bar():
    try:
        safe_input = raw_input
    except NameError:
        safe_input = input
    numstr = safe_input("Enter a positive integer: ")
    ...