How to define a global list in python and append local list to it

Question

I want to define a global list and append a list to it. I am getting a list (i[0]) by some on click event and appended that to mnum_list. Now i want create a global list and append that mnum_list to it. Any idea how to do this?

def OnClick(self, event):                                       
    name = event.GetEventObject().GetLabelText()
    cursor= self.conn.execute("SELECT * FROM ELEMENT where SYMBOL==?", (name,))
    elements = cursor.fetchall()
    print elements
    cursor= self.conn.execute("SELECT ATOMIC_NUMBER FROM ELEMENT where SYMBOL = ?", (name,))
    numbers = cursor.fetchone()[0]
    print numbers
    atomicnumber = numbers
    cursor= self.conn.execute("SELECT MOL_NUMBER FROM LINK where ELEMENT_NUMBER = ?", (atomicnumber,))
    mnumbers = cursor.fetchall()
    print mnumbers
    mnum_list = []
    for i in mnumbers:
         mnum_list.append(i[0])
    print mnum_list

Possible duplicate of Using global variables in a function other than the one that created them — Mike Scotty
– Mike Scotty, Commented Jun 20, 2017 at 6:37
On a side note: I personally consider global variables a design flaw and I would avoid them at all cost if possible. — Mike Scotty
– Mike Scotty, Commented Jun 20, 2017 at 6:39
@mpf82 No, your comment is acting as if global variables are inherently wrong; They aren't. There are perfectly valid use cases for global variables, such as "constant" values. It's when you start trying to use global variables as state that you start getting spaghetti code. — Chris
– Chris, Commented Jun 20, 2017 at 6:43
@mpf82: the OP is trying to manipulate a global. They can just do so without having to know how to use global, because there is no assignment to the global name. — Martijn Pieters
– Martijn Pieters, Commented Jun 20, 2017 at 6:43
If you have a global list (some_global_list = [] at the module level), then just reference it to append to it: some_global_list.append(mnum_list). Mutating a global is that simple. — Martijn Pieters
– Martijn Pieters, Commented Jun 20, 2017 at 6:49

Martijn Pieters · Accepted Answer · 2017-06-20 06:51:27Z

1

There is no need in global statement if there is no assignment, just:

def foo(x):
    sublist = range(x)
    glist.append(sublist)

and in case of extension:

def foo(x):
    sublist = range(x)
    glist.extend(sublist)

edited Jun 20, 2017 at 6:51

Martijn Pieters

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answered Jun 20, 2017 at 6:38

Dimgold

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4 Comments

Martijn Pieters Over a year ago

Mutating a global object doesn't involve assignment, so the global glist line is entirely redundant. Extending doesn't require +=, just use glist.extend() (and += would require the global statement).

Dimgold Over a year ago

right, feels like it will just do the work straightforward.

anon_particle Over a year ago

Sorry i am new to this! Here sublist is mnum_list ?

anon_particle Over a year ago

No its not working! when i print glist it gives me no output pastebin.com/fV9CZQd6

user3732361 · Accepted Answer · 2017-06-20 06:39:43Z

0

You can declare it on the file/module level like: my_global_list = list()

and when you want to append to it inside a function you can use the global keyword. The global keyword tells python to look for the global variable.

global my_global_list

my_global_list.append()

answered Jun 20, 2017 at 6:39

user3732361

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2 Comments

Martijn Pieters Over a year ago

You do not need to use global when mutating an object. That is only required when assigning to a global name.

anon_particle Over a year ago

That worked but didn't solve my problem! Thanks, i have to ask another question

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