Using raw_input in python for lists

Question

I am trying to use raw_input in the python code to get user input of lists as below.

input_array.append(list(raw_input()));

User input as:

1 2 3 5 100

But the code is interpreting input as

[['1', ' ', '2', ' ', '3', ' ', '5', ' ', '1', '0', '0']]

Try: If I use plain input() instead of raw_input(), I am facing the issue in console.

"SyntaxError: ('invalid syntax', ('<string>', 1, 3, '1 2 3 4 100'))"

Note: I am not allowed to give the input in list format like

[1,2,3,5,100]

Could somebody please tell me how to proceed further.

That data looks to you like numbers separated by spaces, but to the computer it's just a string of characters (which happen to be decimal digits and spaces). When you cast it to a list, Python thinks you want a list composing of every individual character in the string. What you want is to separate the string into shorter substrings, using the spaces as the word delimiter; then, turn each substring into an integer and put it in a list. That's what the answer below does. — Andrew Gorcester
– Andrew Gorcester, Commented Dec 5, 2014 at 3:52

jamylak · Accepted Answer · 2014-12-05 04:17:39Z

>>> [int(x) for x in raw_input().split()]
1 2 3 5 100
[1, 2, 3, 5, 100]

>>> raw_input().split()
1 2 3 5 100
['1', '2', '3', '5', '100']

Creates a new list split by whitespace and then

[int(x) for x in raw_input().split()]

Converts each string in this new list into an integer.

list()

is a function that constructs a list from an iterable such as

>>> list({1, 2, 3}) # constructs list from a set {1, 2, 3}
[1, 2, 3]
>>> list('123') # constructs list from a string
['1', '2', '3']
>>> list((1, 2, 3))
[1, 2, 3] # constructs list from a tuple

so

>>> list('1 2 3 5 100')
['1', ' ', '2', ' ', '3', ' ', '5', ' ', '1', '0', '0']

also works, the list function iterates through the string and appends each character to a new list. However you need to separate by spaces so the list function is not suitable.

input takes a string and converts it into an object

'1 2 3 5 100'

is not a valid python object, it is 5 numbers separated by spaces. To make this clear, consider typing

>>> 1 2 3 5 100
SyntaxError: invalid syntax

into a Python Shell. It is just invalid syntax. So input raises this error as well.

On an important side note: input is not a safe function to use so even if your string was '[1,2,3,5,100]' as you mentioned you should not use input because harmful python code can be executed through input. If this case ever arises, use ast.literal_eval:

>>> import ast
>>> ast.literal_eval('[1,2,3,5,100]')
[1, 2, 3, 5, 100]

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