You are using Python 2 for which the input() function tries to evaluate the expression entered. Because you enter a string, Python treats it as a name and tries to evaluate it. If there is no variable defined with that name you will get a NameError exception.
To fix the problem, in Python 2, you can use raw_input(). This returns the string entered by the user and does not attempt to evaluate it.
Note that if you were using Python 3, input() behaves the same as raw_input() does in Python 2.
In Python2, input is evaluated, input() is equivalent to eval(raw_input()). When you enter klj, Python tries to evaluate that name and raises an error because that name is not defined.
Use raw_input to get a string from the user in Python2.
Demo 1: klj is not defined:
>>> input()
klj
Traceback (most recent call last):
File “
File “
NameError: name ‘klj’ is not defined
Demo 2: klj is defined:
>>> klj = ‘hi’
>>> input()
klj
‘hi’
Demo 3: getting a string with raw_input:
>>> raw_input()
klj
‘klj’