Variable scope

There are two scopes: outside of all functions and inside of a function.
The first assignment to a variable defines it.
Variables that were declared outside all functions can be seen inside, but cannot be changed.
One can connect the outside name to an inside name using the 'global' keyword.
if and for blocks don't provide scoping.

a = 23

def main():
    global b
    b = 17
    c = 42
    print('a:', a)    # a: 23
    print('b:', b)    # b: 17
    print('c:', c)    # c: 42

    if True:
        print('a:', a)    # a: 23
        print('b:', b)    # b: 17
        b = 99
        print('b:', b)    # b: 99
        print('c:', c)    # c: 42

    print('a:', a)    # a: 23
    print('b:', b)    # b: 99
    print('c:', c)    # c: 42


main()

print('a:', a)  # a: 23
print('b:', b)  # b: 99
print('c:', c)  # c:
# Traceback (most recent call last):
#  File "examples\basics\scope.py", line 27, in <module>
#    print 'c:', c # c:
# NameError: name 'c' is not defined