Global name in Python

Question

I want to find out whether two numbers N1 and N2 are the permutations of the same digits. For example 123 and 321 are permutations of the same digits, where as 234 and 123 are not. I have used Python to solve the problem of which I am not an expert. I am using IDLE Python GUI on Windows 7. The specifications are Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win32.

The Python code is shown below,

def k(n, m):
    s1 = n
    s2 = m
    k = 0
    fl = 0
    while k < 10 :
        arr1[k] = 0
        arr2[k] = 0
        k = k + 1
    while s1 > 0 :
        t = s1 % 10
        arr1[t] = 1
        t = s2 % 10
        arr2[t] = 1
        s1 = s1 / 10
        s2 = s2 / 10
    k = 0
    while k < 10 :
        if arr1[k] != arr2[k]:
            fl = 1
        k = k + 1
    return fl

I saved the file as k.py and imported using the following command import k. But when I tried to execute the code as k.k(123, 321) I am getting the following error.

Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    k.k(123,321)
  File "k.py", line 7, in k
    global arr2
NameError: global name 'arr1' is not defined

I tried to declare the arrays as follows,

arr1 = []
arr2 = []

I also tried,

global arr1 = []
global arr2 = []

and

global arr1
global arr2

But I am still getting the same error. What is wrong with my code?

I have checked the following answers in SO but I couldn't solve my problem.

Help Defining Global Names

Use of "global" keyword in Python

What I believed was that in Python you don't have to declare any variables, instead you can simply use them. Am I wrong about this assumption?

Any suggestions? Thank you.

Might want to consider `sorted(str(n)) == sorted(str(m))` which is a bit easier to grok — Jon Clements, May 02 '13 at 08:16

Daniel Roseman · Accepted Answer · 2013-05-02T08:55:00.407

3

There is no need to do anything with global values here. Everything should be contained within the function.

The problem is simply that you don't define arr1 or arr2 before you try appending to them. You need to define them in that function, along with s1, s2, k and fl.

Edit I should add that your code is extremely unPythonic. All these while loops with incrementing counters should be replaced with for loops: for k in range(10) etc. But the first loop isn't even necessary - you should have arr1 = [0] * 10 and the same for arr2.

edited May 02 '13 at 08:55

answered May 02 '13 at 08:16

Daniel Roseman

588,541
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+1. How can I define an array? I tried arr1 = [] and arr2 = []. – Deepu May 02 '13 at 08:17
And you did this before you called the function? – Matthias May 02 '13 at 08:20
@DDD: The question is: What is `arr1`? If you define it as an empty list, you can't use `arr1[k] = 0` because there is no element at position `k`. – Matthias May 02 '13 at 08:45
@Matthias while true, that's not the source of OP's error. DDD, are you sure you did that at the start of that function along with your other definitions? Please update your code to show what you did. – Daniel Roseman May 02 '13 at 08:52

score 1 · Answer 2 · answered May 02 '13 at 08:29

1

You need to define the arrays in the functions. And then append to it. arr1 = [] defines an empty array.

arr1[k] = 2

tries to change the value at index k. So either you should initialise it to a certain size or append to the empty array (using the append function).

Also, if you want to access the arrays from outside the function, you might want to return the arrays from the function

answered May 02 '13 at 08:29

nab

191
3
9

+1. But my idea was to use the index to check the presence of digits from 0 to 9. – Deepu May 02 '13 at 08:32
Isn't your first loop an initialisation to 0? use arr1.append(0) instead of the indexing after having created the array as arr1 = []. Or replace the loop by arr1 = [0]*10, which creates an empty array of 10 zeroes. – nab May 02 '13 at 09:00

Global name in Python

2 Answers2