Scope, type and UnboundLocalError

[Paddy]

Hi,
I am trying to work out why I get UnboundLocalError when accessing an
int from a function where the int is at the global scope, without
explicitly declaring it as global but not when accessing a list in
similar circumstances.

The documentation: http://docs.python.org/ref/naming.html does not give
me enough info to determine why the difference exists as it does not
seem to mention types at all..

The code:

===== scope_and_type.py =======
m = 0
n = [0]

def int_access0():
    m = m + 1
    return m
def int_access1():
    m += 1
    return m
def list_access0():
    n[0] = n[0] + 1
    return n
def list_access1():
    n[0] += 1
    return n

try:
    print "\nint_access0:", int_access0()
except UnboundLocalError, inst:
    print " ERROR:\n", inst
try:
    print "\nint_access1:", int_access1()
except UnboundLocalError, inst:
    print " ERROR:\n", inst
try:
    print "\nlist_access0:", list_access0()
except UnboundLocalError, inst:
    print " ERROR:\n", inst
try:
    print "\nlist_access1:", list_access1()
except UnboundLocalError, inst:
    print " ERROR:\n", inst


print "\n (m,n) = ", (m,n)


p = (0,)
def tuple_access():
    return p[0]
try:
    print "\ntuple_acces:", tuple_access()
except UnboundLocalError, inst:
    print " ERROR:\n", inst
print "\n p = ", p

===== END scope_and_type.py =======

The output:
>>>
int_access0:  ERROR:
local variable 'm' referenced before assignment

int_access1:  ERROR:
local variable 'm' referenced before assignment

list_access0: [1]

list_access1: [2]

 (m,n) =  (0, [2])

tuple_acces: 0

 p =  (0,)
>>>

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