What's wrong with the variable ?

Question

a = [1, 2, 3]
a += [4]
print(a) # [1, 2, 3, 4]

b = [1, 2, 3]
def add(n):
print(b) # [1, 2, 3]
b += [n]
add(4) # UnboundLocalError: local variable 'b' referenced before assignment

Answer 1

You can also put global b in the first line of the function, that make b a global variable and now you can use it in that function, if want to use b again in another function you would need to write global b again. It looks like this:

b = [1,2,3]

def add(n):
global b
print(b)
b += [n]

add(4)

Answer 2

Use b.append(n) instead of b+=[n] to avoid UnboundLocalError

Answer 3

Using global is a very useful thing that i discovered learning extra stuff in internet

Answer 4

Solomoni Railoa Thank you, but maybe you missed the point.
The print(b) inside add(n) has already output [1, 2, 3]

Answer 5

Solomoni Railoa Thanks, that's it!

Answer 6

Just make it global

Answer 7

Just try to global the b varable, like:

a = [1, 2, 3]
a += [4]
print(a) # [1, 2, 3, 4]

b = [1, 2, 3]
def add(n):
global b
print(b) # [1, 2, 3]
b += [n]
add(4)