How to pass sys.argv[n] into a function in Python

Question

I am trying to pass "sys.argv[1]" into a function.

#!/usr/bin/env/ python
import sys
def main():
    test(sys.argv[1])
def test(sys.argv[1]):
    print "Hello " + sys.argv[1]

./arg.py World

File "./arg.py", line 5
def test(sys.argv[1]):
            ^
SyntaxError: invalid syntax

Not sure where to go from here after scowering the Interwebs for a few hours. I have also tried to set the "sys.argv[1]" to a variable and tried passing that into the function and still no avail.

Nephelometer

Answer 1

sys.argv[1] returns a string, so you can't add that as a parameter/argument.

I don't see why you would need this, just put no arguments at all:

def test():
    print "Hello " + sys.argv[1]

---

You may have also gotten mixed up. Argument names do not need to be the same name as what you would use when calling the function. For example, if I had n = 5, the function does not need to have an argument called n. It can be anything.

So you can do:

def test(myargument):
    print "Hello " + myargument

---

I'm just going to give you a quick little "tutorial" on arguments.

def myfunc():
    print "hello!"

Here we have a function. To call it, we do myfunc(), yes? When we do myfunc(), it prints "hello!".

Here is another function:

def myfunc(word):
    print word

This function takes an argument. So when we call it, we have to add an argument. Here's an example of calling the function:

def myfunc(word):
    print word

myword = 'cabbage'
myfunc(myword)

Notice how 'cabbage' is set in the myword variable. It does not have to be the same as what we called the argument in the function. Infact, we don't even have to create a variable if we need. We can just do myfunc('cabbage').

Also, in this example, you can only input one argument, as when we defined the function, we only used one parameter. If you add two, you'll get something like myfunc takes one argument (two given).

We called the argument word so we can use that in the function. Notice how I have print word and not print myword. It's as if we did word = myword, but instead of doing that step, we use the argument name.

Baskett

Okay, basically what I am trying to do with the arguments, is pass a few arguments through that will be called quite a few times. Should I use raw_input / input to set those variables? – Nephelometer

@GregRobertDutertre I think you're misunderstanding the point of arguments – Baskett

Most likely. I also think I may be going about re-learning Python the wrong way as well. – Nephelometer

@GregRobertDutertre I added some more to my answer. I hope this helps! – Baskett

@GregRobertDutertre Good to hear! If you have any further questions, go ahead and ask – Baskett

Answer 2

I think you misunderstand the declaration and call of a function. In your program,there is only declaration,missing the calling statement. As for passing parameters from command line,here is an example which I prefer:

import sys
def hello(v):
    print 'hello '+v

def main(args):
    hello(args[1])

if __name__ == '__main__':
    main(sys.argv)

The program start to execute from the line 'if name == 'main' by calling the function defined previously and passing the sys.argv as parameter

Semantics