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Python shell showing error but cmd is running that program

I am new in python.I am doing addition of two numbers in cmd using input parameter .I am getting output on cmd but getting Error on python shell.I am using windows 7 and python shell 3.3.2 . so anyone can tell me why my code is not running on python shell ?
code:
import sys
n=int(sys.argv[1])
m=int(sys.argv[2])
print(n+m)
Error:
Traceback (most recent call last):
File "C:/pythonprogram/add.py", line 4, in
n=int(sys.argv[1])
IndexError: list index out of range

Your program is expecting two command line arguments.
sys.argv is a list of command line arguments. The error IndexError: list index out of range is telling you that you tried to get list item number 2, (with index 1), but the list doesn't have that many values.
You can reproduce that error in the shell:
>> alist = ['Item 0']
>> print(alist[1])
Since alist only has item with index 0 requesting items with higher indexes will cause that error.
Now, to your exact problem. The program is telling you it expected command line arguments, but they were not provided. Provide them!
Run this command:
python add.py 1 2
This will execute the script and pass 1 as the first argument, 2 as the second argument.
In your case the general format is
python add.py [n] [m]
Now at that point you might be (you should be) wondering what sys.argv[0] is then, any why your n number doesn't get assigned to sys.argv[1].
sys.argv[0] is the name of the script running.
Further reading on command line arguments:
http://www.pythonforbeginners.com/system/python-sys-argv
Additional.
You could modify your script to be more descriptive:
import sys
if len(sys.argv) < 3: #script name + 2 other arguments required
print("Provide at least two numbers")
else:
n=int(sys.argv[1])
m=int(sys.argv[2])
print(n+m)

sys.argv contains the command line parameters. When you run your script in the Python shell you're most likely not sending any parameters. I would suggest adding a check if there are command line arguments present like this:
import sys
if len(sys.argv) > 2:
n=int(sys.argv[1])
m=int(sys.argv[2])
print(n+m)
Check this out to find out more about Python and sys.argv

How to use a argument variable argv?

I wrote the following command but I don't understand it.
from sys import argv
what is argv?
how to use it?
I wrote sycript,a,b=argv
but I am getting the error that need more than one value to unpack.

argv - The list of command line arguments passed to a Python script.
sycript,a,b=argv gives you "ValueError: need more than 1 value to unpack" because you have just run the script as python <script_name.py> without giving the two arguments.
Run the script like this: python <script_name.py> <arg1> <arg2>
For example,
script.py:
from sys import argv
arg,a,b=argv
print(arg,a,b)
run script.py "arg1" "arg2" and output:
script.py arg1 arg2

I think you should run the command by typing
python scriptname a b
By scriptname I mean the name by which you have saved the program code.
I hope this helps..

ValueError: not enough values to unpack (expected 4, got 1)

The error is at script, first, second, third = argv. I would like to understand why I am getting the error and how to fix it.
from sys import argv
script, first, second, third = argv
print("The script is called: ", script)
print("The first variable is: ", first)
print("The second variable is: ", second)
print("The third variable is: ", third)

Run it from the shell like this:
python script.py arg1 arg2 arg3

argv variable contains command line arguments. In your code you expected 4 arguments, but got only 1 (first argument always script name). You could configure arguments in pycharm. Go to Run -> Edit Configurations. Then create a new python configuration. And there you could specify Script parameters field. Or you could run your script from command line as mentioned by dnit13.

You could run it like this: python script.py first, second, third

I think you are running the following command:
python script.py
You are writing a program which is aksing for 4 inputs and you are giving onle one. That's why you are receiving an error. You can use the below command:
python script.py Hello How Are

what is a commandline argument?

I am a newcomer to python (also very sorry if this is a newb question but) i have no idea what a command line argument is. when sys.argv is called, what exactly are the arguments? Any help with understanding this would be a great service.

Try running this program:
import sys
print(sys.argv)
You should see results similar to this:
% test.py
['/home/unutbu/pybin/test.py']
% test.py foo
['/home/unutbu/pybin/test.py', 'foo']
% test.py foo bar
['/home/unutbu/pybin/test.py', 'foo', 'bar']
% python test.py foo
['test.py', 'foo']
So, you see sys.argv is a list. The first item is the path to (or filename of) the script being run, followed by command-line arguments.

Given the command myscript.py arg1 arg2 arg3, the arguments are arg1, arg2 and arg3. sys.argv will also include the script name (i.e. myscript.py) in the first position.
Command line arguments are not specific to python.

Command line arguments are parameters you type after the script name. Eg. if you type: python test.py arg1, the first argument is arg1.
For examples, take a look at jhu.edu.

The command line arguments are the strings you type after a command in the command line, for instance:
python --help
Here --help is the argument for the python command, that shows a help page with the valid command line arguments for the python command.
In a python program, you have access to the arguments in sys.argv, so let's say you started a python script like this:
python myscript.py -x -y
When myscript.py starts, sys.argv[1] will have as value the string '-x' and sys.argv[2] will have as value the string '-y'. What you do with those arguments is up to you, and there are modules to help you easily define command line arguments, for instance argparse.

The arguments are usually used as a way of telling the program what it should do when it is run.
If I had a program named writefile.py, and I wanted the user to tell it which file to write, then I would run it with python writefile.py targetfile.txt. My sample writefile.py:
import sys
file = open(sys.argv[1], 'w') # sys.argv[0] = 'writefile.py' (unutbu's answer)
file.write('ABCDE')
file.close
After running this, I'll have a file named targetfile.txt with the contents "ABCDE". If I ran it with python writefile.py abcde.txt, I'd have abcde.txt with the contents "ABCDE".

What does "sys.argv[1]" mean? (What is sys.argv, and where does it come from?)

I'm currently teaching myself Python and was just wondering (In reference to my example below) in simplified terms what the sys.argv[1] represents. Is it simply asking for an input?
#!/usr/bin/python3.1
# import modules used here -- sys is a very standard one
import sys
# Gather our code in a main() function
def main():
print ('Hello there', sys.argv[1])
# Command line args are in sys.argv[1], sys.argv[2] ..
# sys.argv[0] is the script name itself and can be ignored
# Standard boilerplate to call the main() function to begin
# the program.
if __name__ == '__main__':
main()
You may have been directed here because you were asking about an IndexError in your code that uses sys.argv. The problem is not in your code; the problem is that you need to run the program in a way that makes sys.argv contain the right values. Please read the answers to understand how sys.argv works.
If you have read and understood the answers, and are still having problems on Windows, check if Python Script does not take sys.argv in Windows fixes the issue. If you are trying to run the program from inside an IDE, you may need IDE-specific help - please search, but first check if you can run the program successfully from the command line.

I would like to note that previous answers made many assumptions about the user's knowledge. This answer attempts to answer the question at a more tutorial level.
For every invocation of Python, sys.argv is automatically a list of strings representing the arguments (as separated by spaces) on the command-line. The name comes from the C programming convention in which argv and argc represent the command line arguments.
You'll want to learn more about lists and strings as you're familiarizing yourself with Python, but in the meantime, here are a few things to know.
You can simply create a script that prints the arguments as they're represented. It also prints the number of arguments, using the len function on the list.
from __future__ import print_function
import sys
print(sys.argv, len(sys.argv))
The script requires Python 2.6 or later. If you call this script print_args.py, you can invoke it with different arguments to see what happens.
> python print_args.py
['print_args.py'] 1
> python print_args.py foo and bar
['print_args.py', 'foo', 'and', 'bar'] 4
> python print_args.py "foo and bar"
['print_args.py', 'foo and bar'] 2
> python print_args.py "foo and bar" and baz
['print_args.py', 'foo and bar', 'and', 'baz'] 4
As you can see, the command-line arguments include the script name but not the interpreter name. In this sense, Python treats the script as the executable. If you need to know the name of the executable (python in this case), you can use sys.executable.
You can see from the examples that it is possible to receive arguments that do contain spaces if the user invoked the script with arguments encapsulated in quotes, so what you get is the list of arguments as supplied by the user.
Now in your Python code, you can use this list of strings as input to your program. Since lists are indexed by zero-based integers, you can get the individual items using the list[0] syntax. For example, to get the script name:
script_name = sys.argv[0] # this will always work.
Although interesting, you rarely need to know your script name. To get the first argument after the script for a filename, you could do the following:
filename = sys.argv[1]
This is a very common usage, but note that it will fail with an IndexError if no argument was supplied.
Also, Python lets you reference a slice of a list, so to get another list of just the user-supplied arguments (but without the script name), you can do
user_args = sys.argv[1:] # get everything after the script name
Additionally, Python allows you to assign a sequence of items (including lists) to variable names. So if you expect the user to always supply two arguments, you can assign those arguments (as strings) to two variables:
user_args = sys.argv[1:]
fun, games = user_args # len(user_args) had better be 2
So, to answer your specific question, sys.argv[1] represents the first command-line argument (as a string) supplied to the script in question. It will not prompt for input, but it will fail with an IndexError if no arguments are supplied on the command-line following the script name.

sys.argv[1] contains the first command line argument passed to your script.
For example, if your script is named hello.py and you issue:
$ python3.1 hello.py foo
or:
$ chmod +x hello.py # make script executable
$ ./hello.py foo
Your script will print:
Hello there foo

sys.argv is a list.
This list is created by your command line, it's a list of your command line arguments.
For example:
in your command line you input something like this,
python3.2 file.py something
sys.argv will become a list ['file.py', 'something']
In this case sys.argv[1] = 'something'

Just adding to Frederic's answer, for example if you call your script as follows:
./myscript.py foo bar
sys.argv[0] would be "./myscript.py"
sys.argv[1] would be "foo" and
sys.argv[2] would be "bar" ... and so forth.
In your example code, if you call the script as follows ./myscript.py foo , the script's output will be "Hello there foo".

Adding a few more points to Jason's Answer :
For taking all user provided arguments: user_args = sys.argv[1:]
Consider the sys.argv as a list of strings as (mentioned by Jason). So all the list manipulations will apply here. This is called "List Slicing". For more info visit here.
The syntax is like this: list[start:end:step]. If you omit start, it will default to 0, and if you omit end, it will default to length of list.
Suppose you only want to take all the arguments after 3rd argument, then:
user_args = sys.argv[3:]
Suppose you only want the first two arguments, then:
user_args = sys.argv[0:2] or user_args = sys.argv[:2]
Suppose you want arguments 2 to 4:
user_args = sys.argv[2:4]
Suppose you want the last argument (last argument is always -1, so what is happening here is we start the count from back. So start is last, no end, no step):
user_args = sys.argv[-1]
Suppose you want the second last argument:
user_args = sys.argv[-2]
Suppose you want the last two arguments:
user_args = sys.argv[-2:]
Suppose you want the last two arguments. Here, start is -2, that is second last item and then to the end (denoted by :):
user_args = sys.argv[-2:]
Suppose you want the everything except last two arguments. Here, start is 0 (by default), and end is second last item:
user_args = sys.argv[:-2]
Suppose you want the arguments in reverse order:
user_args = sys.argv[::-1]

sys.argv is a list containing the script path and command line arguments; i.e. sys.argv[0] is the path of the script you're running and all following members are arguments.

To pass arguments to your python script
while running a script via command line
> python create_thumbnail.py test1.jpg test2.jpg
here,
script name - create_thumbnail.py,
argument 1 - test1.jpg,
argument 2 - test2.jpg
With in the create_thumbnail.py script i use
sys.argv[1:]
which give me the list of arguments i passed in command line as
['test1.jpg', 'test2.jpg']

sys.argv is a attribute of the sys module. It says the arguments passed into the file in the command line. sys.argv[0] catches the directory where the file is located. sys.argv[1] returns the first argument passed in the command line. Think like we have a example.py file.
example.py
import sys # Importing the main sys module to catch the arguments
print(sys.argv[1]) # Printing the first argument
Now here in the command prompt when we do this:
python example.py
It will throw a index error at line 2. Cause there is no argument passed yet. You can see the length of the arguments passed by user using if len(sys.argv) >= 1: # Code.
If we run the example.py with passing a argument
python example.py args
It prints:
args
Because it was the first arguement! Let's say we have made it a executable file using PyInstaller. We would do this:
example argumentpassed
It prints:
argumentpassed
It's really helpful when you are making a command in the terminal. First check the length of the arguments. If no arguments passed, do the help text.

sys.argv will display the command line args passed when running a script or you can say sys.argv will store the command line arguments passed in python while running from terminal.
Just try this:
import sys
print sys.argv
argv stores all the arguments passed in a python list. The above will print all arguments passed will running the script.
Now try this running your filename.py like this:
python filename.py example example1
this will print 3 arguments in a list.
sys.argv[0] #is the first argument passed, which is basically the filename.
Similarly, argv[1] is the first argument passed, in this case 'example'.