Variable scope

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• 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.

examples/basics/scope.py

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