input（）错误-NameError：名称“ …”未定义

I am getting an error when I try to run this simple script:

input_variable = input ("Enter your name: ")
print ("your name is" + input_variable)

Let’s say I type in “dude”, the error I am getting is:

line 1, in <module>
input_variable = input ("Enter your name: ")
File "<string>", line 1, in <module>
NameError: name 'dude' is not defined

I am running these scripts with Python 2.7.

TL;DR

input function in Python 2.7, evaluates whatever your enter, as a Python expression. If you simply want to read strings, then use raw_input function in Python 2.7, which will not evaluate the read strings.

If you are using Python 3.x, raw_input has been renamed to input. Quoting the Python 3.0 release notes,

raw_input() was renamed to input(). That is, the new input() function reads a line from sys.stdin and returns it with the trailing newline stripped. It raises EOFError if the input is terminated prematurely. To get the old behavior of input(), use eval(input())

In Python 2.7, there are two functions which can be used to accept user inputs. One is input and the other one is raw_input. You can think of the relation between them as follows

input = eval(raw_input)

Consider the following piece of code to understand this better

>>> dude = "thefourtheye"
>>> input_variable = input("Enter your name: ")
Enter your name: dude
>>> input_variable
'thefourtheye'

input accepts a string from the user and evaluates the string in the current Python context. When I type dude as input, it finds that dude is bound to the value thefourtheye and so the result of evaluation becomes thefourtheye and that gets assigned to input_variable.

If I enter something else which is not there in the current python context, it will fail will the NameError.

>>> input("Enter your name: ")
Enter your name: dummy
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "<string>", line 1, in <module>
NameError: name 'dummy' is not defined

Security considerations with Python 2.7’s input:

Since whatever user types is evaluated, it imposes security issues as well. For example, if you have already loaded os module in your program with import os, and then the user types in

os.remove("/etc/hosts")

this will be evaluated as a function call expression by python and it will be executed. If you are executing Python with elevated privileges, /etc/hosts file will be deleted. See, how dangerous it could be?

To demonstrate this, let’s try to execute input function again.

>>> dude = "thefourtheye"
>>> input("Enter your name: ")
Enter your name: input("Enter your name again: ")
Enter your name again: dude

Now, when input("Enter your name: ") is executed, it waits for the user input and the user input is a valid Python function invocation and so that is also invoked. That is why we are seeing Enter your name again: prompt again.

So, you are better off with raw_input function, like this

input_variable = raw_input("Enter your name: ")

If you need to convert the result to some other type, then you can use appropriate functions to convert the string returned by raw_input. For example, to read inputs as integers, use the int function, like shown in this answer.

In python 3.x, there is only one function to get user inputs and that is called , which is equivalent to Python 2.7’s raw_input.

You are running Python 2, not Python 3. For this to work in Python 2, use raw_input.

input_variable = raw_input ("Enter your name: ")
print ("your name is" + input_variable)

Since you are writing for Python 3.x, you’ll want to begin your script with:

#!/usr/bin/env python3

If you use:

#!/usr/bin/env python

It will default to Python 2.x. These go on the first line of your script, if there is nothing that starts with #! (aka the shebang).

If your scripts just start with:

#! python

Then you can change it to:

#! python3

Although this shorter formatting is only recognized by a few programs, such as the launcher, so it is not the best choice.

The first two examples are much more widely used and will help ensure your code will work on any machine that has Python installed.

You should use raw_input because you are using python-2.7. When you use input() on a variable (for example: s = input('Name: ')), it will execute the command ON the Python environment without saving what you wrote on the variable (s) and create an error if what you wrote is not defined.

raw_input() will save correctly what you wrote on the variable (for example: f = raw_input('Name : ')), and it will not execute it in the Python environment without creating any possible error:

input_variable = raw_input('Enter Your Name : ')
print("Your Name Is  : " + (input_variable))

For python 3 and above

s = raw_input()

it will solve the problem on pycharm IDE if you are solving on online site exactly hackerrank then use:

s = input()

You could either do:

x = raw_input("enter your name")
print "your name is %s " % x

or:

x = str(input("enter your name"))
print "your name is %s" % x

input_variable = input ("Enter your name: ")
print ("your name is" + input_variable)

You have to enter input in either single or double quotes

Ex:'dude' -> correct

    dude -> not correct

I also encountered this issue with a module that was supposed to be compatible for python 2.7 and 3.7

what i found to fix the issue was importing:

from six.moves import input

this fixed the usability for both interpreters

you can read more about the six library here

We are using the following that works both python 2 and python 3

#Works in Python 2 and 3:
try: input = raw_input
except NameError: pass
print(input("Enter your name: "))

For anyone else that may run into this issue, turns out that even if you include #!/usr/bin/env python3 at the beginning of your script, the shebang is ignored if the file isn’t executable.

To determine whether or not your file is executable:

• run ./filename.py from the command line
• if you get -bash: ./filename.py: Permission denied, run chmod a+x filename.py
• run ./filename.py again

If you’ve included import sys; print(sys.version) as Kevin suggested, you’ll now see that the script is being interpreted by python3

Good contributions the previous ones.

import sys; print(sys.version)

def ingreso(nombre):
    print('Hi ', nombre, type(nombre))

def bienvenida(nombre):
    print("Hi "+nombre+", bye ")

nombre = raw_input("Enter your name: ")

ingreso(nombre)
bienvenida(nombre)

#Works in Python 2 and 3:
try: input = raw_input
except NameError: pass
print(input("Your name: "))

Enter your name: Joe
('Hi ', 'Joe', &lttype 'str'&gt)
Hi Joe, bye 

Your name: Joe
Joe

Thanks!

There are two ways to fix these issues,

• 1st is simple without code change that is
  run your script by Python3,
  if you still want to run on python2 then after running your python script, when you are entering the input keep in mind

  1. if you want to enter string then just start typing down with “input goes with double-quote” and it will work in python2.7 and
  2. if you want to enter character then use the input with a single quote like ‘your input goes here’
  3. if you want to enter number not an issue you simply type the number

• 2nd way is with code changes
  use the below import and run with any version of python

  1. from six.moves import input
  2. Use raw_input() function instead of input() function in your code with any import
  3. sanitise your code with str() function like str(input()) and then assign to any variable

As error implies:
name ‘dude’ is not defined i.e. for python ‘dude’ become variable here and it’s not having any value of python defined type assigned
so only its crying like baby so if we define a ‘dude’ variable and assign any value and pass to it, it will work but that’s not what we want as we don’t know what user will enter and moreover we want to capture the user input.

Fact about these method:
input() function: This function takes the value and type of the input you enter as it is without modifying it type.
raw_input() function: This function explicitly converts the input you give into type string,

Note:
The vulnerability in input() method lies in the fact that the variable accessing the value of input can be accessed by anyone just by using the name of variable or method.

You can change which python you’re using with your IDE, if you’ve already downloaded python 3.x it shouldn’t be too hard to switch. But your script works fine on python 3.x, I would just change

print ("your name is" + input_variable)

to

print ("your name is", input_variable)

Because with the comma it prints with a whitespace in between your name is and whatever the user inputted. AND: if you’re using 2.7 just use raw_input instead of input.