Global variable in Python

Question

I've been reading a Python textbook, and I see the following code:

class Database:
# the database implementation
    pass

database = None

def initialize_database():
    global database
    database = Database()

Now, why is there a global declaration inside initialize_database function? We had defined database outside the function, doesn't it make it global already?

Best Regards,

http://stackoverflow.com/questions/423379/global-variables-in-python — Pavan Yalamanchili, May 07 '11 at 23:21

score 9 · Answer 1 · answered May 07 '11 at 23:20

9

You can reference a global when it's not declared global in a function, but you can only read it; writing it will create a new local variable hiding the global variable. The global declaration makes it able to write to the global.

answered May 07 '11 at 23:20

icktoofay

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I think you may have meant "Yes, it is already a global." rather than "No." – ninjagecko May 07 '11 at 23:24
@ninjagecko: I'll just get rid of the yes/no at the beginning. – icktoofay May 07 '11 at 23:25

score 1 · Answer 2 · answered May 08 '11 at 00:15

'global x' doesn't make x global, it should be read as "from now on in this namespace, treat all references to x as as references to x in a higher namespace."

Remember you're not permanently doing anything to x, your just making x point to something different within a function.

Global variable in Python

2 Answers2