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Recently i came across a question & confused with a possible solution, code part is 

// code part in result reader
result = map(int, input())
// consumer call
result_consumer(result)

its not about how do they work, the problem is when you are running in python2 it will raise an exception, on result fetching part, so result reader can handle the exception, but incase of python3 a map object is returned, so only consumer will be able to handle exception. is there any solution keeping map function & handle the exception in python2 & python3

python3

>>> d = map(int, input())
1,2,3,a
>>> d
<map object at 0x7f70b11ee518>
>>>

python2

>>> d = map(int, input())
1,2,3,'a'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'a'
>>>
Renjith Thankachan
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    Aside from the `map` thing, you have an entirely different bug in that `input` doesn't work that way on Python 3. – user2357112 Dec 11 '16 at 19:55

3 Answers3

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If you always need the exception to occur at the same place you can always force the map object to yield its results by wrapping it in a list call:

result = list(map(int, input()))

If an error occurs in Python 2 it will be during the call to map while, in Python 3, the error is going to surface during the list call.

The slight downside is that in the case of Python 2 you'll create a new list. To avoid this you could alternatively branch based on sys.version and use the list only in Python 3 but that might be too tedious for you.

Dimitris Fasarakis Hilliard
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  • The "dowsnside" you mention is a complete non-issue - you are making a single function call - of the orders of a few micro-seconds, in response to the user typing an input - soemhting that takes on the order of seconds. – jsbueno Dec 12 '16 at 14:08
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the behavior of map is not the only difference between python2 and python3, input is also difference, you need to keep in mind the basic differences between the two to make code compatible for both

python 3 vs python 2
  map    =   itertools.imap
  zip    =   itertools.izip
  filter =   itertools.ifilter
  range  =   xrange
  input  =   raw_input

so to make code for both, you can use alternatives like list comprehension that work the same for both, and for those that don't have easy alternatives, you can make new functions and/or use conditional renames, like for example

my_input = input
try: 
    raw_input
except NameError: #we are in python 3
    my_input = lambda msj=None: eval(input(msj))

(or with your favorite way to check which version of python is in execution)

# code part in result reader
result = [ int(x) for x in my_input() ]
# consumer call
result_consumer(result)

that way your code do the same regardless of which version of python you run it.

But as jsbueno mentioned, eval and python2's input are dangerous so use the more secure raw_input or python3's input

try: 
    input = raw_input
except NameError: #we are in python 3
    pass

(or with your favorite way to check which version of python is in execution)

then if your plan is to provide your input as 1,2,3 add an appropriate split

# code part in result reader
result = [ int(x) for x in input().split(",") ]
# consumer call
result_consumer(result)
Community
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Copperfield
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    Please - do the other way around, and overrite Python's 2 broken input with Python3 working input. Your try-except thing just recreates the broken behavior in Python3 where it does not exist. – jsbueno Dec 12 '16 at 14:06
  • @jsbueno what did you mean? change the my_input to raw_input?? I do it that way because it looks like the OP is using py2 as its main and I try to make the behavior the same for both versions – Copperfield Dec 12 '16 at 15:01
  • "try: raw_input else: input=raw_input` - tht makes the Python3 well behaved version of input to be in place of the insecure and bizarre Python2 input. – jsbueno Dec 12 '16 at 15:13
  • @jsbueno I add that to the my answer – Copperfield Dec 12 '16 at 15:33
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I usually use my own version of map in this situations to escape any possible problem may occur and it's 

def my_map(func,some_list):
    done = []
    for item in some_list:
        done.append( func(item) )
    return done

and my own version of input too

def getinput(text):
    import sys
    ver = sys.version[0]
    if ver=="3":
        return input(text)
    else:
        return raw_input(text)

if you are working on a big project add them to a python file and import them any time you need like what I do.

D4Vinci
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