UNBOUNDLOCALERROR

Question

I am relatively new to python and I can't understand why does this throws an error.

ar=''
def decToBin(no):
    while(no>0):
        ar=ar+str(no%2)
        no=no//2
    print(ar[::-1])
decToBin(4)

code that works

def decToBin(no):
    ar=''
    while(no>0):
        ar=ar+str(no%2)
        no=no//2
    print(ar[::-1])
decToBin(4)

The scope of the "ar" variable is supposed to be global and should be accessible inside the function. Can anyone explain why the former isn't working?

Does this answer your question? [Why does python behave this way with variables?](https://stackoverflow.com/questions/48192290/why-does-python-behave-this-way-with-variables) — Maximouse, Jan 31 '20 at 07:15

Dean · Answer 1 · 2020-01-31T07:49:33.557

0

Changing decimal to binary is easy with numpy:

import numpy as np
np.binary_repr(4, width=None)

edited Jan 31 '20 at 07:49

answered Jan 31 '20 at 07:41

Dean

103
1
9

You import as `np` but then try to use `numpy.binary_repr` – Justin Ezequiel Jan 31 '20 at 07:44

score -1 · Answer 2 · answered Jan 31 '20 at 07:35

-1

The issue is this line:

ar=ar+str(no%2)

You are referencing it, before it has been assigned.

Try this instead:

ar = ''
def decToBin(no):
    while(no>0):
        #ar=ar+str(no%2)
        no=no//2
    print((ar+str(no%2))[::-1])
decToBin(4)

answered Jan 31 '20 at 07:35

Dean

103
1
9

Did you actually try running that? What did it print out? – Justin Ezequiel Jan 31 '20 at 07:42
Yep. Printed '0'. – Dean Jan 31 '20 at 07:52
So do you think 0 is the base 2 representation of 4? – Justin Ezequiel Jan 31 '20 at 07:53
No of course not, but that's not the question is it.... – Dean Jan 31 '20 at 07:56
So you give a wrong answer that does not raise an exception. How is that helpful to the OP? – Justin Ezequiel Jan 31 '20 at 07:58

UNBOUNDLOCALERROR

2 Answers2